Question

The configuration of R-(+)-glyceraldehyde is as follows: o II C-H H-I-OH CH2OH What is the configuration of (-)-lactic acid? COH H-OH CH2OH O R configuration O S configuration d and/configuration O Rand S configuration O configuration

Answer 1

The answer is A.

We use the CIP Rules to identify that the -OH group has the highest priority, followed by the -COOH group, -CH₂OH group and finally the -H group. Now, since the -H (the group with the lowest preference) is not present at the lower vertical bond, we swap -H and -CH₂OH. Since we must swap in pairs to ensure that the resulting compound is equivalent to the original, we swap the -OH and the -COOH groups as well. We can now check the direction in which the preference order 1 - 2 - 3 - 4 occurs. This gives us the R configuration (clockwise).

co OON Swap H 1 OH OH Swap CH₂OH = OH ® CH₂OH- COOH a direction of preference Clockwise) Hence, R H