Addition to Carbon-Oxygen Double Bonds *
protonated 2,4,6-trimethylbenzoic acid cannot as the o-methyl groups
prevent the atoms of the carboxyl group from lying in the same
plane as the benzene ring and IT orbital interaction is thus much
reduced or prevented. With the acylium ion (LII) however, there is no
such restriction and the substituent methyl groups can indeed further
delocalise the positive charge by hyperconjugation:
O
" H
eI
CH,(ill) Addition reactions of nitriles
Nitrites also undergo nucleophilic addition reactions due to:© ©
—OpN: ~ —C=N:
(/
Tires they will ifWergo acid-catalysed addition of ethanol to yield
salts of imino-ethers (LIV)
HOEt OEt
H© © EtOH I I ©
R—OsN ===== R—C=NH >• R—C=NH ===== R—C=NH,
(LIV)and also acid or base catalysed addition of water:R—C=NH
H®/* \(i)H,OOH O
/ (u)-H©\ | ||
R—C=N R—C=NH R—C—NH,
\ OH /
©OH\ J /H,O
R—C=N
It is often difficult to isolate trie amide, however, for this undergoes
readier hydrolysis than the original nitrite yielding the acid or its
anion.
Nitriles will, of course, also undergo addition of Grignard reagents
to yield ketones and of hydrogen to yield primary amines.