The correct order of decreasing value of `K_(eq)` is :

Options

A. `agtbgtcgtd`
B. `dgtagtbgtc`
C. `dgtbgtagtc`
D. `dgtagtcgtd`

Answer

B

Explanation

In simple nucleophilic additions where the rate-limiting step is attack by `Y^(ө)` the positive character of the carbonyl carbon atom is reduced on going from the starting material (5) to the transition state (6) :

We should thus expect the rate of addition to be reduced by electron-donating R groups and enhanced by electron-withdrawing ones, this is borne out by the observed sequence :

In the above examples steric, as well as electronic, effect could be influencing relative rates of reaction, but the influence of electronic effects alone may be seen in the series of compounds (11):
So far as steric effects are concerned, the least energy demanding direction of approach by the nucleophile to the carbonyl carbon atom will be from above, or below, the substantially planar carbonyl compound. It is also likely to be from slightly to the rear of the carbon atom, because of potential coulombic repulsion between the approaching nucleophile and the high electron density at the carbonyl oxygen atom:
Thus the Ks for cyanohydrin formation are found to reflect this operation of both steric and electronic factors:

Highly hindered ketones, such as `Me_(3)C COCMe_(3)` may not react at all except possibly with very small, highly reactive nucleophilies.