http://s74.beta.photobucket.com/user/tey…
-
Nucleophilic attack will be preferable at carbon N.
The relative reactivities of aldehydes in nucleophilic addition reactions may be attributed to the amount of positive charge on the carbon. A greater positive charge means a higher reactivity. If the positive charge is dispersed throughout the molecule, the carbonyl compound becomes more stable and its reactivity decreases. Alkyl groups are electron releasing groups - the electron releasing power of CHR2 at carbon O is more than that of CH2R at carbon N. As a result, the electron deficiency of carbon O is satisfied more than carbon N. Therefore, the reduced positive charge on carbon O discourages the attack of nucleophiles. Hence carbon O is less susceptible to nucleophilic attack than carbon N.
Additionally, the size of the alkyl group attached to carbon O (CHR2) is greater than that attached to carbon N (CHR2). Alkyl groups are larger than hydrogen atoms and cause steric hindrance to the attacking group. As the number and size of the alkyl groups increase, the hindrance to nucleophilic attack also increases and the reactivity of the carbonyl decreases. Less hindrance at carbon N is another reason for its greater susceptibility to nucleophilic attack.
The relative reactivities of aldehydes in nucleophilic addition reactions may be attributed to the amount of positive charge on the carbon. A greater positive charge means a higher reactivity. If the positive charge is dispersed throughout the molecule, the carbonyl compound becomes more stable and its reactivity decreases. Alkyl groups are electron releasing groups - the electron releasing power of CHR2 at carbon O is more than that of CH2R at carbon N. As a result, the electron deficiency of carbon O is satisfied more than carbon N. Therefore, the reduced positive charge on carbon O discourages the attack of nucleophiles. Hence carbon O is less susceptible to nucleophilic attack than carbon N.
Additionally, the size of the alkyl group attached to carbon O (CHR2) is greater than that attached to carbon N (CHR2). Alkyl groups are larger than hydrogen atoms and cause steric hindrance to the attacking group. As the number and size of the alkyl groups increase, the hindrance to nucleophilic attack also increases and the reactivity of the carbonyl decreases. Less hindrance at carbon N is another reason for its greater susceptibility to nucleophilic attack.