Term
| a reaction in which one group displaces another is known as? |
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Definition
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Term
| name the five major electrophilic substitutions of benzene? |
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Definition
- halogenation
- nitration
- sulphonation
- friedel-crafts alkylation
- friedel-crafts acylation
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Term
| what is a species (usually cationic) that can form a bond to a carbon by accepting an electron pair? |
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Definition
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Term
| what is a species (anionic or neutral) that can form a bond to a carbon by donating an electron pair? |
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Definition
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Term
| name the reaction whereby an intial electrophile attack leads to an addition reaction. |
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Definition
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Term
| name the reaction whereby an electrophile attack leads in a sustitution reaction? |
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Definition
| electrophilic substitution |
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Term
| electrophilic aromatic substitution (EAS) is a how many step process? |
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Definition
3 step process
1. a postively charged electrophile generated
2. benzene ring attacks electrophile generating a resonance carbocation
3. the carbocation lose a h+ to give an aromatic product
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Term
in generating the electrophile from Br-Br for EAS, how is the bond cleaved?
what facilitates this cleavage and how does it help? |
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Definition
heterolytic cleavage (uneven sharing)
FeBr3 catalysts helps by acting as a Lewis base and accepting a bromide ion. |
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Term
| in EAS an intermediate carbocation is formed. is this intermediate carbocation aromatic? over how many electrons is the charge delocalised over? |
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Definition
the intermediate carbocation is NOT aromatic
the charge of the carbocation is delocalised over THREE specific carbons of the ring |
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Term
| what is the name of the delocalised non aromatic intermediate carbocation in EAS? |
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Definition
arenium ion
only FOUR electrons are in the delocalised pi system of an arenium ion |
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Term
| what is the hybridisation of the arenium ion? |
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Definition
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Term
| from the electrophilic addition, resonance stabilised cation and the rearomatisation stage, which of these steps is the fastest? |
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Definition
| the re-aromatisation stage |
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Term
| what is required for halogenation of benzene? |
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Definition
| a lewis acid catalyst - it facilitates the formation of an electrophile by acting as a halid anion acceptor |
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Term
| what reagents are needed for nitration of benzene? |
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Definition
| concentrated nitric and sulphuric acid |
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Term
| what is the electrophile in nitration of benzene? |
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Definition
NO2+ nitronium ion
this is formed from nitric acid by PROTONATION followed by LOSS of H20 |
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Term
| what is the role of sulphuric acid in nitration of benzene? |
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Definition
| to force a proton onto nitric acid. |
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Term
| which reagent is used in the sulphonation of benzene? |
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Definition
SO3 dissolved in concentrated sulphuric acid.
this reagent is also known as OLEUM |
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Term
| what is the electrophile used in sulphonation of benzene? |
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Definition
SO3H+
the SO3 is protonated by H2SO4 |
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Term
| in Friedel-Crafts Acylation, an acyl group is introduced by reaction with an acid chloride in the presence of which catalyst? |
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Definition
| AlCl3 - this acts as a halide anion acceptor allowing the acyl (electrophile) cation to form. |
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Term
| how are acid chlorides made? |
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Definition
| they are made from the corresponding acid by reacting it with Thionyl Chloride (SOCl2). the products are acid chloride, sulphur dioxide and HCl |
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Term
| in Friedel-Crafts Acylation, the acylated benzene is a ......... |
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Definition
| ketone baby! its a ketone! |
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Term
| which reaction is similar to Friedel-Craft Acylation but uses an alkyl chloride instead? |
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Definition
| Friedel-Craft Alkylation. the AlCl3 catalyst is still used and has the same role to accept a halid ion to allow the formation of an electrophile. |
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Term
| what complications arise from Friedel-Craft Alkylations involving primary carbocations? |
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Definition
| carbocation ion rearrangement. A primary carbocation can undergo rapid HYDROGEN SHIFT to form a more stable secondary carbocation before the aromatic attacks it |
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Term
| if you really wanted to put a linear alkyl chain onto benzene how would you get around the rapid hydrogen shift? |
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Definition
do a Friedel-Craft acylation and then reduce the C=O group.
A clemmensen reduction reduces an acyl group into an alkyl group. |
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Term
| what does a clemmenson reduction do and what reagents does it involve? |
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Definition
it reduces an acyl group into an alkyl group and involves
Zn (Hg) / HCl |
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Term
what can nitrobenzene be converted into by
Sn/HCl (aq)
followed by alkaline work up? |
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Definition
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Term
what can benzene sulphonic acid get converted into by
NaOH (s) and heat
followed by acid work up? |
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Definition
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Term
| oxidation of alkylbenzene with acidified dichromate gives which product? |
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Definition
benzoic acid.
acidified dichromate > Na2Cr2O7 /H2SO4
H20 and heat |
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