The correct order of decreasing value of K_eq  is 

In simple TE:"4itic_additions where the .rate-limiting step is attack by ${\mathrm{Y}}^{\ominus }$ , the positive character of the carbonvl carbon atom is reduced on going from the starting Material(5); the transition state (6):

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

In the above examples of steric as well as electronic effect could be influencing relative rates seen in the series of compounds (11) :
So far as steric effects are concerned, the least energy - demanding direction of approach by nucleophile to the  carbonyl compound. It is also likely to be from slightly to the rear of the carbon atom, because ot Potential coulombic repulsion between the approaching nucleophile and the high electron density at the carbonyl orygen atom :
Thus the K_s for cyanohydrin formation are found to reflect this operation of both steric and t.^ erectronlc tactors:

Highly hindered ketones, such as Me₃CCOCMe₃, may not react at all except possibly with very small, highly reactive nucleophilies.