Term
| An __________ __________ simply has a halogen atom bonded to one of the sp3 hybrid carbon atoms of an alkyl group. |
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Definition
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|
Term
| A __________ __________ has a halogen atom bonded to one of the sp2 hybrid carbon atoms of an alkene. |
|
Definition
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|
Term
| An __________ __________ has a halogen atom bonded to one of the sp2 hybrid carbon atoms of an aromatic ring. |
|
Definition
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|
Term
| The carbon-halogen bond in an alkyl halide is __________ because halogen atoms are more __________ than carbon atoms. |
|
Definition
1) Polar
2) Electronegative |
|
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Term
| A carbon atom has a partial __________ charge, making it __________; a nucleophile can attack this __________ carbon, and the __________ atom can leave as a halide ion, taking the bonding pair of electrons with it. |
|
Definition
1) Positive
2) Electrophile
3) Electrophilic
4) Halogen |
|
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Term
| A compound of formula CH2X2 (a methylene group with two halogens) is called a __________ __________; a compound of formula CHX3 is called a __________; and a compound of formula CX4 is called a __________ __________. |
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Definition
1) Methylene halide
2) Haloform
3) Carbon tetrahalide |
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Term
__________ __________ are classified according to the nature of the carbon atom bonded to the halogen.
-If the halogen-bearing carbon is bonded to one carbon atom, it is primary (1°) and the alkyl halide is a __________ __________.
-If two carbon atoms are bonded to the halogen-bearing carbon, it is secondary (2°) and the compound is a __________ __________.
-A __________ __________ (3°) has three other carbon atoms bonded to the halogen-bearing carbon atom.
-If the halogen-bearing carbon atom is a methyl group (bonded to no other carbon atoms), the compound is a __________ __________. |
|
Definition
1) Alkyl halide
2) Primary halide
3) Secondary halide
4) Tertiary halide
5) Methyl halide |
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Term
A __________ __________ (Latin, geminus "twin") has two halogens bonded to the same carbon.
A __________ __________ (Latin, vicinus, "neighboring") has the two halogens bonded to adjacent carbon atoms. |
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Definition
1) Geminal dihalide
2) Vicinal dihalde |
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Term
| __________ (also called chloroflourocarbons, or CFCs) are flourinated haloalkanes that were developed to replace ammonia as a refrigerant gas. |
|
Definition
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Term
In an alkyl halide, the halogen atom is bonded to an __________ hybrid carbon atom.
The halogen is more __________ than carbon, and the C-X bond is __________ with a partial __________ charge on carbon and a partial __________ charge on the halogen. |
|
Definition
1) Sp3
2) Electronegative
3) Polarized
4) Positive
5) Negative |
|
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Term
The __________ of the halogens increase in the order:
I < Br < Cl < F |
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Definition
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|
Term
The carbon-halogen __________ __________ increase as the halogen atoms become __________ in the order:
C-F < C-Cl < C-Br < C-I |
|
Definition
|
|
Term
Bond __________ __________ increase in the general order:
C-I < C-Br < C-F < C-Cl |
|
Definition
|
|
Term
| A __________ __________ __________ is the vector sum of the individual bond dipole moments. |
|
Definition
| 1) Molecular dipole moments |
|
|
Term
| The __________ __________ __________ is the strongest intermolecular attraction in alkyl halides. |
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Definition
| 1) London dispersion force |
|
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Term
Molecules with large __________ __________ have higher London attractions, resulting in higher boiling points.
Molecules with higher __________ __________ also generally have higher boiling points because they are heavier and have greater __________ __________.
Compounds that are __________ and have __________ __________ also have lower boiling points as a result of their smaller surface areas. |
|
Definition
1) Surface areas
2) Molecular weights
3) Surface areas
4) Branched
5) Spherical shapes |
|
|
Term
| Alkyl __________ and __________ are less dense than water; alkyl __________ and __________ are more dense than water. |
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Definition
1) Flourides
2) Chlorides
3) Bromides
4) Iodides |
|
|
Term
| An __________ position is a carbon atom next to a carbon-carbon double bond. __________ intermediates are stabilized by __________ with the double bond, allowing the charge of the radical to be delocalized. |
|
Definition
1) Allylic
2) Allylic
3) Resonance |
|
|
Term
| A bromine radical abstracts an __________ __________ atom to give a resonance-stabilized allylic radical. |
|
Definition
|
|
Term
| The second product of an allylic bromination results from a reaction at the carbon atom that bears the radical in the second resonance form of the __________ __________; this second compound is said to be the product of an __________ __________. |
|
Definition
1) Allylic radical
2) Allylic shift |
|
|
Term
| N-Bromosuccinimide (__________) is often used as the __________ source in free-radical brominations because it combines with the HBr side product to regenerate a constant low concentration of bromine. |
|
Definition
|
|
Term
When a halogen atom can leave with its bonding pair of electrons to form a stable halide ion we categorize that halide as a good __________ __________.
-When another atom replaces a halide ion, the reaction is known as a __________.
-When a halide ion leaves with another atom or ion (often H+) the reaction is an __________.
-In many eliminations a molecule of H-X is lost from the alkyl halide to produce an alkene; an __________ reaction known as a __________ as a hydrogen has been removed from the alkyl halide. |
|
Definition
1) Leaving group
2) Substitution
3) Elimination
4) Elimination
5) Dehalogenation |
|
|
Term
| In a __________ __________, a nulceophile replaces a leaving group from a carbon atom, using its lone pair of electrons to forma new bond to the carbon atom. |
|
Definition
| 1) Nucleophilic substitution |
|
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Term
| In an __________ both the halide ion and another substituent are lost; the result if the formation of a __________ bond. |
|
Definition
|
|
Term
In the reaction of hydroxide with iodomethane to produce methanol, the hydroxide ion is a strong __________ (donor of an electron pair) because the oxygen atom has unshared pairs of __________ and a __________ charge.
In this scenario, iodomethane is the __________, or the compound attacked by the reagent.
The carbon atom of iodometan is __________ because it is bonded to an electronegative iodine atom.
__________ __________ is generally drawn away from the carbon by the halogen atom, giving the carbon atom a partial positive charge. |
|
Definition
1) Nucleophile
2) Electrons
3) Negative
4) Substrate
5) Electrophilic
6) Electron density |
|
|
Term
| In SN2 reactions, the rate is found to __________ when the concentration of __________ reactant is doubled. |
|
Definition
|
|
Term
| The SN3 abbreviation stands for __________, __________, __________. The term __________ means that the transition state of the rate-limiting step (the ONLY step in this reaction) involves the collision of __________ molecules. |
|
Definition
1) Substitution, Nucleophilic, bimolecular
2) Bimolecular
3) Two |
|
|
Term
The SN2 reaction of methyl iodide with hydroxide ion is a __________ __________, taking place in __________ step with bonds breaking and forming at the same time.
The middle form is a __________ __________, a point of __________ energy rather than an intermediate. |
|
Definition
1) Concerted reaction
2) One
3) Transition state
4) Maximum |
|
|
Term
| In SN2 reactions, the __________ __________ is much higher in energy than any reactant or product because it involves a five-coordinate carbon atom with two partial bonds. |
|
Definition
|
|
Term
The order of reactivity for substrates in an __________ reaction is:
CH3X > 1° > 2° (3° alkyl halides cannot occur) |
|
Definition
|
|
Term
| Halides can be converted to other halides by __________ __________ __________, in which one halide displaces another. |
|
Definition
| 1) Halogen exchange reactions |
|
|
Term
| For SN2 reactions, a __________ nucleophile is much more effective than a __________ one in attacking an electrophilic carbon atom; a species with a __________ charge is a stronger nucleophile than a species with a __________ charge. |
|
Definition
1) Strong
2) Weak
3) Negative
4) No or zero |
|
|
Term
| *A __________ is always a stronger nucleophile than its __________ __________.* |
|
Definition
|
|
Term
| __________ is defined by the equilibrium constant for abstracting a proton, while __________ is defined by the rate of attack on an electrophilic carbon atom. If a new bond is formed to a proton it has reacted as a __________; if a new bond is to carbon, it has reacted as a __________. |
|
Definition
1) Basicity
2) Nucleophilicity
3) Base
4) Nucleophile |
|
|
Term
*Trends in Nucleophilicity:
1. A species with a __________ charge is stronger than a similar species with a __________ charge. In particular, a __________ is a stronger nucleophile than its __________ __________.
2) Nucleophilicity __________ from left to right in the periodic table, following the __________ in electronegativity from left to right. The more __________ elements have more tightly held nonbonding electrons that are __________ reactive toward forming new bonds.
3) Nucleophilicity __________ down the periodic table, following the __________ in size and polarizability, and the __________ in electronegativity. |
|
Definition
1A) Negative
1B) No or zero
1C) Base
1D) Conjugate acid
2A) Decreases
2B) Increase
2C) Electronegative
2D) Less
3A) Increases
3B) Increase
3C) Decrease |
|
|
Term
| As we go down a column in the periodic table, the atoms become __________, with more electrons at a greater distance from the nucleus. The electrons are more loosely held, and the atom is more __________: it's electrons can move more freely toward a positive charge, resulting in stronger bonding in the __________ __________. |
|
Definition
1) Larger
2) Polarizable
3) Transition state |
|
|
Term
| The __________ the bonding between carbon and the halogen in the transition state, the __________ the energy of the transition state. |
|
Definition
|
|
Term
| When bulky groups with interfere with a reaction by virtue of their size, we call the effect __________ __________. |
|
Definition
|
|
Term
Steric hindrance has little effect on __________ because __________ involves attack on an unhindered proton. When a __________ attacks a carbon atom, however, a __________ __________ cannot approach the carbon atom so easily.
-If we want a species to act as a __________, we use a __________ reagent like ter-butoxide ion.
-If we want it to react as a __________, we use a __________ __________ reagent, like ethoxide. |
|
Definition
1) Basicity
2) Basicity
3) Nucleophile
4) Bulky nucleophile
5) Base
6) Bulky
7) Nucleophile
8) Less hindered |
|
|
Term
| A __________ __________ is one that has acidic protons, usually in the form of O-H or N-H groups. These groups form hydrogen bonds to negatively charged __________. |
|
Definition
1) Protic solvent
2) Nucleophiles |
|
|
Term
| __________ anions are solvated more strongly than __________ anions in a protic solvent because the solvent approaches a small anion more closely and forms stronger __________ __________. More energy is required to strip off solvent from a __________, strongly solvated ion than from a __________ diffuse, less strongly solvated ion. |
|
Definition
1) Small
2) Large
3) Hydrogen bonds
4) Small
5) Larger |
|
|
Term
| In protic solvents, polarizability __________ with increasing atomic number, and the solvation energy __________ with increasing atomic number. Therefore, nucleophilicity generally __________ down a column in the periodic table. |
|
Definition
1) Increases
2) Decreases
3) Increases |
|
|
Term
| __________ __________ enhance the nucleophilicity of anions as an anion is more reactive in an __________ __________ because it is not so strongly solvated (does not require large amounts of energy to break hydrogen bonds). |
|
Definition
1) Aprotic solvents
2) Aprotic solvents |
|
|
Term
__________ __________ __________ have strong dipole moments to enhance solubility, yet they have no O-H or N-H groups to form __________ __________ with anions.
Specific solvating reagents are added to enhance the __________ of a reaction without affecting the reactivity of the __________. |
|
Definition
1) Polar aprotic solvents
2) Hydrogen bonds
3) Solubility
4) Nucleophile |
|
|
Term
| The alkyl halide is often referred to as the __________ or the compound being attacked by the reagent. |
|
Definition
|
|
Term
A leaving group serves two purposes in the SN2 reaction:
1. It __________ the C-X bond, making the carbon atom __________.
2. It leaves with the pair of __________ that once bonded it to the __________ carbon atom.
To fill these roles, a good leaving group should be:
1. __________ withdrawing, to polarize the carbon atom,
2. Stable (not a strong __________) once it has left, and
3. __________ to stabilize the transition state. |
|
Definition
1A) Polarizes
1B) Electrophilic
2A) Electrons
2B) Electrophilic
1AA) Electron
2AA) Base
3AA) Polarizable |
|
|
Term
| __________ __________ are strongly electronegative, making common substrates for SN2 reactions along with __________, __________, and __________ which form strongly polarized bonds with carbon. |
|
Definition
1) Halogen atoms
2) Nitrogen
3) Oxygen
4) Sulfur |
|
|
Term
| In SN2 reactions (and generally), a reactive leaving group raises the energy of the __________ __________ and the __________, driving the equilibrium forward. |
|
Definition
1) Transition state
2) Products |
|
|
Term
| Good leaving groups should be __________ bases; they are therefore the __________ __________ of strong acids. The hydrohalic acids (HCl, HBr, and HI) are strong acids and their __________ __________ (Cl-, Br-, I-) are all __________ bases. __________, __________, and __________ ions also serve as good leaving groups. |
|
Definition
1) Weak
2) Conjugate bases
3) Conjugate bases
4) Weak
5) Sulfate
6) Sulfonate
7) Phosphate |
|
|
Term
| __________ and __________ ions and other strong bases are poor leaving groups for SN2 reactions. |
|
Definition
|
|
Term
| A neutral molecule often serves as the leaving group from a __________ __________ species. |
|
Definition
|
|
Term
In SN2 reactions, a good leaving group should be __________ to maintain partial bonding with the carbon atom in the transitions state.
This bonding helps stabilize the __________ __________ and reduce the __________ __________. |
|
Definition
1) Polarizable
2) Transition State
3) Activation energy |
|
|
Term
For simple alkyl halides, the relative rates for __________ displacement are:
CH3X > 1° > 2° >> 3° (does not occur) |
|
Definition
|
|
Term
| In SN2 reactions, even a bulky __________ __________ (like neopentyl bromide) undergoes SN2 reactions at a rate similar to that of a __________ __________ |
|
Definition
1) Primary halide
2) Tertiary halide |
|
|
Term
| The SN2 reaction requires attack by a nucleophile on the __________ __________ of the __________ carbon atom. |
|
Definition
1) Back side
2) Electrophilic |
|
|
Term
| During an SN2 reaction, __________-__________ __________ literally turns the tetrahedron of the carbon atom inside out, like an umbrella caught by the wind. In the product, the nucleophile assumes a stereochemical position __________ the position the leaving group originally occupied; this is known as __________ __________ __________ at the carbon atom. |
|
Definition
1) Back-side attack
2) Opposite
3) Inversion of configuration |
|
|
Term
| The SN2 displacement (back-side attack) is the most common example of a __________ __________, a step (in a reaction sequence) where an __________ carbon atom undergoes inversion of configuration. |
|
Definition
1) Walden inversion
2) Asymmetric |
|
|
Term
| SN2 displacement is a good example of a __________ __________ in which different stereoisomers react to give different stereoisomers of the product. |
|
Definition
| 1) Stereospecific reaction |
|
|
Term
*To study the mechanism of a nucleophilic substitution, we often look at the product to see if the reaction is stereospecific.
-If it is, the __________ mechanism is a good possibility, especially if the reaction kinetics are __________ order. |
|
Definition
|
|
Term
| A reaction which characterizes the SN1 mechanism in which a solvent acts as a nucleophile is known as a __________. |
|
Definition
|
|
Term
| In SN1 reactions, the rate depends only on the concentration of the __________. |
|
Definition
|
|
Term
| The SN1 reaction stands for __________, __________, and__________, where the term __________ means there is only one molecule involved in the transition state of the rate-limiting step. |
|
Definition
1) Substitution
2) Nucleophilic
3) Unimolecular
4) Unimolecular |
|
|
Term
| The SN1 mechanism is a multistep process: The first step is a slow __________ to form a __________; the second step is a __________ attack on the carbocation by a __________; the final step is the loss of a __________ to the original solvent. |
|
Definition
1) Ionization
2) Carbocation
3) Fast
4) Nucleophile
5) Proton
5) |
|
|
Term
| The nucleophiles in an SN1 reaction are usually __________, as a strong nucleophile would be more likely to attack the __________ and force some kind of second-order reaction. |
|
Definition
|
|
Term
*The SN1 Reaction*
The SN1 reaction involves a __________-step mechanism. A __________ ionization gives a carbocation that reacts quickly with a (usually __________) nucleophile. The reactivity of __________ reactions is:
3° > 2° > 1°
-Step 1: Formation of the __________ (rate-limiting)
-Step 2: Nucleophilic attack on the __________ (fast).
IF THE NUCLEOPHILE IS WATER OR AN ALCOHOL, A THIRD STEP IS NEEDED TO DEPROTONATE THE PRODUCT.
-Step 3: __________ to form the product. |
|
Definition
1) Two
2) Slow
3) Weak
4) SN1
S1) Carbocation
S2) Carbocation
S3) Deprotonation |
|
|
Term
| In an SN1 reaction, the __________ step is highly (endothermic/exothermic) and its large activation energy determines the overall reaction rate. The __________ step is strongly (endothermic/exothermic) with a lower-energy transition state. |
|
Definition
1) First
2) Endothermic
3) Second
4) Exothermic |
|
|
Term
| The __________-__________ step of the __________ reaction is ionization to form a carbocation, a strongly (endothermic/exothermic) process. |
|
Definition
1) Rate-determining
2) SN1 |
|
|
Term
| Rates of SN1 reactions depend strongly on __________ stability. |
|
Definition
|
|
Term
Alkyl groups stabilize carbocations by donating electrons through sigma bonds (the __________ ___________) and through overlap of filled orbitals with the empty p orbital of the carbocation (__________). Highly substituted __________ are therefore the most stable:
3° > 2° > 1° > CH3X |
|
Definition
1) Inductive effect
2) Hyperconjugation
3) Carbocations |
|
|
Term
| Alkyl groups hinder the __________ by blocking attack of the strong nucleophile, but alkyl groups enhance the __________ by stabilizing the carbocation intermediate. |
|
Definition
|
|
Term
| __________ and __________ halides generally do not undergo SN1 or SN2 reactions; a __________ reaction would require ionization to form a __________ or __________ cation, either of which is less stable than most __________ carbocations. |
|
Definition
1) Vinyl
2) Aryl
3) SN2
4) Vinyl
5) Aryl
6) Alkyl |
|
|
Term
In SN1 reactions, a highly __________ leaving group helps stabilize the __________-__________ transition state through partial bonding as it leaves.
The leaving group should be a __________ base, very stable after it leaves with the pair of electrons that bonded it to the __________ atom. |
|
Definition
1) Polarizble
2) Rate-limiting
3) Weak
4) Carbon |
|
|
Term
| The SN1 reaction goes much more readily in __________ solvents that stabilize ions. The rate-limiting step forms __________ ions, and ionization takes place in the __________ __________. Polar solvents solvate these ions by interaction of the solvent's __________ __________ with the __________ of the ion. __________ solvents such as alcohols and water are even more effective solvents due to the hydrogen bonds that can be formed with the anions. |
|
Definition
1) Polar
2) Two
3) Transition state
4) Dipole moment
5) Charge
6) Protic |
|
|
Term
| SN1 reactions require highly __________ solvents that strongly solvate ions. |
|
Definition
|
|
Term
| One measure of a solvent's ability to solvate ion is its __________ __________, a measure of the solvent's polarity. |
|
Definition
|
|
Term
| In the SN1 mechanism the reaction is not __________: the carbocation intermediate is __________ hybridized and __________; a nucleophile is able to attack the carbocation from either face. |
|
Definition
1) Stereospecific
2) Sp2
3) Planar |
|
|
Term
| A process in which both enantiomers of a product are possible (whether or not the two enantiomers are produced in equal amounts) is called __________. |
|
Definition
|
|
Term
| In SN1 reactions, if a nucleophile attacks a carbocation from the front side, the product molecule shows __________ __________ __________; attack from the back side gives a product molecule showing __________ __________ __________. __________ is simply a combination of retention and inversion. |
|
Definition
1) Retention of configuration
2) Inversion of configuration
3) Racemization |
|
|
Term
| In SN1 reactions, when racemization occurs, there is often more __________ than __________ of configuration; this is because the __________ __________ often blocks the front side of the carbocatiion, leaving the back side open and thus __________ more likely. |
|
Definition
1) Inversion
2) Retension
3) Leaving group
4) Inversion |
|
|
Term
Carbocations frequently undergo structural changes, called __________, to form more stable ions.
A __________ may occur after a __________ has formed or it may occur as the __________ __________ is leaving. __________ do not occur in SN2 reactions because no carbocation is formed, making the process impossible. |
|
Definition
1) Rearrangements
2) Rearrangement
3) Carbocation
4) Leaving group
5) Rearrangements |
|
|
Term
| A __________ __________ is the movement of a hydrogen atom with its bonding pair of electrons. The __________ __________ converts the initially formed __________ (level) carbocation to a more stable __________ (level) carbocation). |
|
Definition
1) Hydride shift
2) Hydride shift
3) Secondary
4) Tertiary |
|
|
Term
*Hydride Shift in an SN1 Reaction:
-Step 1: Unimolecular ionization gives a __________.
-Step 2: A __________ __________ forms a more stable carbocation
-Step 3: A solvent (__________ nucleophile) attacks the rearranged carbocation.
-Step 4: __________ gives the rearranged product. |
|
Definition
1) Carbocation
2) Hydride shift
3) Weak
4) Deprotonation |
|
|
Term
| A __________ __________ is another rearrangement characterized by the migration of a methyl group together with its pair of electrons. |
|
Definition
|
|
Term
*Methyl Shift in an SN1 Reaction:*
-Step 1: Ionization occurs with a __________ __________.
NOTE: THE SHIFT OCCURS WHILE THE BROMIDE ION IS LEAVING, UNLIKE THE HYDRIDE SHIFT WHICH OCCURS IN TWO SEPARATE STEPS.
-Step 2: Attack by ethanol gives a __________ version of the rearranged product.
-Step 3: __________ gives the rearranged product. |
|
Definition
1) Methyl shift
2) Protonated
3) Deprotonation |
|
|
Term
*Effect of the Nucleophile on SN1/SN2:*
SN1: Nucleophile strength is unimportant (usually __________).
SN2: __________ nucleophiles are required |
|
Definition
|
|
Term
*Effect of the Substrate on SN1/SN2:*
__________ Substrates: 3° > 2° (1° and CH3X are unlikely)
__________ Substrates: CH3X > 1° > 2° (3° is impossible). |
|
Definition
|
|
Term
*Effect of the Solvent on SN1/SN2:*
SN1: Strong __________ and __________ __________ ionizing solvents such as alcohols and waters are needed.
SN2: Reactions go faster in less __________ solvents and in __________ __________ solvents. |
|
Definition
1) Polar
2) Polar protic
3) Polar
4) Polar aprotic |
|
|
Term
*Kinetics of SN1/SN2:*
SN1: Rate is proportional to the concentration of the __________ __________ but not the concentration of the __________; follows first-order rate equation.
SN2: Rate is proportional to the concentrations of both the __________ __________ and the __________. |
|
Definition
1) Alkyl halide
2) Nucleophile
3) Alkyl halide
4) Nucleophile |
|
|
Term
*Stereochemistry of SN1/SN2:*
SN1: Reactions involve flat __________ intermediate that can be attacked from either face; gives mix of __________ and __________ (__________) products.
SN2: Reactions take place through back-side attack only, leading to complete __________. |
|
Definition
1) Carbocation
2) Retension
3) Inversion
4) Racemization
5) Inversion |
|
|
Term
*Rearrangements of SN1/SN2:*
SN1: Carbocation intermediate can rearrange by __________ or __________ __________ to produce a more stable carbocation.
SN2: There is no carbocation intermediate so rearrangements are not possible. |
|
Definition
1) Hydride shift
2) Alkyl shift |
|
|
Term
| An __________ involves the loss of two atoms or groups from the substrate, usually with the formation of a __________ bond. |
|
Definition
|
|
Term
| The abbreviation E1 stands for __________ __________. The mechanism is termed __________ because the rate-limiting transition state involves a __________ molecule rather than a collision between __________ molecules. |
|
Definition
1) Elimination
2) Unimolecular
3) Unimolecular
4) Single
5) Two |
|
|
Term
*The E1 Reaction:*
The E1 reaction requires ionization to a carbocation intermediate like the __________ reaction, so it follows the same order of reactivity:
3° > 2° >> 1°. However, in an E1 reaction a base (usually __________) deprotonates the carbocation to produce an __________.
-Step 1: Unimolecular ionization to produce a __________ (rate-limiting).
-Step 2: __________ by a __________ base produces an alkene (fast). |
|
Definition
1) SN1
2) Weak
3) Alkene
4) Carbocation
5) Deprotonation
6) Weak |
|
|
Term
| The E1 mechanism is different than the SN1 mechanism in that the __________ base deprotonates the carbocation to produce an __________. |
|
Definition
|
|
Term
| In E1 reactions, the rate depends only on the concentration of the __________ __________ and not on the strength or concentration of the base. |
|
Definition
|
|
Term
| In E1 reactions, a __________ reaction is an elimination of a hydrogen and halogen atom. |
|
Definition
|
|
Term
In the second step of the E1 mechanism, the carbon atom next to the C+ must rehybridize to __________ as the __________ attacks the protons and electrons flow into the new __________ orbital.
The potential-energy diagram for E1 mechanisms is similar to that of SN2: The ionization (first) step is strongly (endothermic/exothermic), with a rate-limiting __________ __________. The second step is a fast (endothermic/exothermic) deprotonation by a __________. |
|
Definition
1) Sp2
2) Base
3) Pi
4) Exothermic
5) Transition state
6) Endothermic
7) Base |
|
|
Term
*Rearrangement in the E1 Reaction:*
-Step 1: __________ to form a carbocation (slow).
-Step 2: A __________ __________ forms a more stable carbocation (fast).
-Step 3: The __________ basic solvent removes either adjacent proton (__________). |
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Definition
1) Ionization
2) Hydride shift
3) Weakly
4) Fast |
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Term
*Summary: Carbocation Reactions:*
A carbocation can:
1. React with its own __________ __________ to return to the reactant.
2. React with a __________ to form a substitution product (SN1).
3. Lose a __________ to form an elimination product (an __________; E1).
4. __________ to a more stable carbocation to react further. |
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Definition
1) Leaving group
2) Nucleophile
3) Proton
4) Alkene
5) Rearrange |
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Term
| In most E1 and E2 eliminations where there are two or more possible elimination products; the product with the most substituted __________ __________ will predominate; this principle is called __________ __________ and reactions that give this desired alkene are said to follow __________ __________. |
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Definition
1) Double bond
2) Zaitsev's rule
3) Zaitsev orientation |
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Term
*__________ __________ states that in elimination reactions, the most substituted alkene usually predominates:
R2C=CR2 > R2C=CHR > RHC=CHR or R2C=CH2 > RHC=CH2 |
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Definition
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Term
| The abbreviation E2 stands for __________ __________; in this process the rate is proportional to both the concentrations of the __________ __________ and the __________, giving a second-order orientation. |
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Definition
1) Elimination
2) Bimolecular
3) Alkyl halide
4) Base |
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Term
| In the general mechanism of the E2 reaction, a strong __________ abstracts a proton on a carbon atom adjacent to the one with the __________ __________; as this occurs a __________ __________ is formed and the leaving group leaves. |
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Definition
1) Base
2) Leaving group
3) Double bond |
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Term
| Like the SN2 reaction, the E2 elimination is a __________ reaction in which bonds break and form at the same time in a __________ step. |
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Definition
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Term
*Reactivity of the Substrate in the E2:*
The order of reactivity of alkyl halides toward E2 dehydrohalogenation is found to be:
__________ > __________ > __________
This reactivity order reflects the greater stability of highly substituted __________ __________. |
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Definition
1) 3°
2) 2°
3) 1°
4) Double bonds |
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Term
*Mixtures of Products in the E2:*
The E2 reaction requires abstraction of a proton on a __________ atom NEXT to the carbon bearing the halogen. In most cases, __________ __________ predicts that the major product will be the most substituted alkene. |
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Definition
1) Carbon
2) Zaitsev's Rule |
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Term
| Like the SN2 reaction, the E2 reaction follows a __________ __________ in which bond breaking and forming occur simultaneously, with partial formation of new bonds lowering the energy of the __________ __________. For the reaction to be successful a specific geometric arrangement is required: for SN2 reactions it is a __________ -__________ __________ attack; for E2 reactions it is a __________ arrangement of orbitals. |
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Definition
1) Concerted mechanism
2) Transition state
3) Back-side attack
4) Coplanar |
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Term
| The E2 elimination requires partial formation of a new __________ bond with its parallel __________ orbitals in the transition state. The electrons that once formed a C-H bond must begin to overlap with the orbital that the __________ __________ is vacating. Formation of this new __________ bond implies that two __________ orbitals must be parallel so that __________ overlap is possible as the hydrogen and halogen leave and the orbitals rehybridize to the __________ orbitals of the new pi bond. |
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Definition
1) Pi
2) P
3) Leaving group
4) Pi
5) P
6) Pi
7) P |
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Term
In an E2 elimination reaction, when the hydrogen and halogen are __________ to one another (0 = 180°) their orbitals are aligned; this is known as __________-__________ conformation.
When the hydrogen and halogen eclipse one another (0 = 0°), their orbitals are once again aligned; this is the __________-__________ conformation.
The __________-__________ (0 = 180) is staggered and has the __________ energy while the __________-__________ is eclipsed and has the __________ energy. |
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Definition
1) Anti
2) Anti-coplanar
3) Syn-coplanar
4) Anti-coplanar
5) Lowest
6) Syn-coplanar
7) Highest |
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Term
| In E2 reactions, the __________-__________ conformation is the most stable and the __________-__________ conformation is the least stable. |
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Definition
1) Anti-coplanar
2) Syn-coplanar |
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Term
| Molecules that are rigidly held in eclipsed (__________-__________) conformations with a hydrogen and leaving group are most likely to leave through a __________-__________ concerted mechanism. |
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Definition
1) Syn-coplanar
2) Syn-coplanar |
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Term
| The E2 elimination reaction is a __________ reaction because different stereoisomers of the starting material react to produce different stereoisomers of the product. |
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Definition
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Term
*Effect of the Base in E1/E2:*
__________: Base strength is unimportant (usually __________)
__________: Requires __________ base. |
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Definition
1) E1
2) Weak
3) E2
4) Strong |
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Term
*Effect of the Solvent in E1/E2:*
E1: Requires a good __________ solvent or __________ __________ solvent such as water or alcohol.
E2: Solvent __________ is not very important; strong base still reacts in very __________ solvent. |
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Definition
1) Polar
2) Polar protic
3) Polarity
4) Nonpolar |
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Term
*Effect of the Substrate on E1/E2:*
For both E1 and E2 reactions, the order of reactivity is:
__________ > __________ > __________ (1° will usually not go __________).
E1: Rate-limiting step is formation of __________ and reactivity reflects stability of __________.
E2: More substituted halides generally form more stable __________. |
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Definition
1) 3°
2) 2°
3) 1°
4) E1
5) Carbocation
6) Carbocation
7) Alkene |
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Term
*Kinetics of E1/E2:*
E1: Rate is proportional to the concentration of __________ __________; follows first-order rate equation.
E2: Rate is proportional to both concentrations of __________ __________ and __________; follow second-order rate equation. |
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Definition
1) Alkyl halide
2) Alkyl halide
3) Base |
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Term
*Orientation of Elimination for E1/E2:*
In most E1 and E2 eliminations with two or more products; the product with most substituted __________ __________ (most stable) predominates; principle known as __________ __________ and the most highly substituted product is __________ __________. |
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Definition
1) Double bond
2) Zitsev's Rule
3) Zitsev product |
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Term
*Stereochemistry of E1/E2:*
E1: No particular geometry required.
E2: Takes places through __________ mechanism which requires a __________ arrangement of the bonds to the atoms being eliminated. Transition state is usually __________-__________ although it may be __________-__________ in rigid systems (eclipsed). |
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Definition
1) Concerted
2) Coplanar
3) Anti-coplanar
4) Syn-coplanar |
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Term
*Rearrangements in E1/E2:*
E1: Carbocation intermediate can perform rearrangement through __________ or __________ __________ to produce a more stable carbocation.
E2: No rearrangements possible (concerted mechanism). |
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Definition
1) Hydride shift
2) Alkyl shift |
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Term
*Predicting Substitutions and Eliminations*
1. The strength of the __________ or __________ determines the order of the reaction.
-If a strong __________ (or ___________) is present, it will force second-order kinetics, either SN2 or E2. A strong nucleophile attacks the electrophilic __________ atom or abstracts a __________ faster than the molecule can ionize for first-order reactions. |
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Definition
1) Nucleophile
2) Base
3) Nucleophile
4) Base
5) Carbon
6) Proton |
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Term
*Predicting Substitutions and Eliminations*
2. Primary halides usually undergo the __________ reaction, occasionally the __________ reaction.
-Primary halides rarely undergo first-order reactions, since primary carbocations are rarely formed. With good nucleophiles __________ is usually observed; with a strong base __________ may be observed. |
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Definition
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Term
| Sometimes __________ __________ or __________ temperatures are used to force a PRIMARY halide to ionize usually with rearrangement to form a more stable carbocation. In these instances,rearranged __________ and __________ products are observed. |
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Definition
1) Silver salts
2) High
3) SN1
4) E1 |
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Term
*Predicting Substitutions and Eliminations*
3. __________ halides usually undergo the E2 reaction (__________ base) or a mixture of SN1 and E1 (__________ base).
-Tertiary halides cannot undergo the __________ reaction. A __________ base forces second-order kinetics by the E2 mechanism; in the absence of the base tertiary halides react by first-order processes. |
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Definition
1) Tertiary
2) Strong
3) Weak
4) SN2
5) Strong |
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Term
*Predicting Substitutions and Eliminations*
4. The reactions of __________ halides are the most difficult to predict. |
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Definition
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Term
*Predicting Substitutions and Eliminations*
5. Some nucleophiles and bases favor substitution or elimination.
-To promote elimination, the __________ should readily abstract a proton but not readily attack a carbon atom. A bulky strong __________, such as tert-butoxide enhances elimination. __________ temperatures also favor elimination in most cases as more molecules are formed.
To promote substitution, we need a good __________ with limited basicity: a highly __________ species that is the conjugate base of a strong acid. |
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Definition
1) Base
2) Base
3) High
4) Nucelophile
5) Polarizable |
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