c. Isoleucine has a carbon “branched” closer to the alpha carbon than does leucine.
The structure of leucine is CH3CH(<u>CH3</u>)CH2CH(NH2)COOH.
The structure of isoleucine is CH3CH2CH(<u>CH3</u>)CH(NH2)COOH.
In leucine, the CH3 group is <em>two carbons away</em> <em>from</em> the α carbon; in isoleucine, the CH3 group is on the carbon <em>next to</em> the α carbon.
Thus, <em>isoleucine</em> has the closer branched carbon.
“One is charged, the other is not” is i<em>ncorrect</em>. Both compounds are uncharged.
“One has more H-bond acceptors than the other” is <em>incorrect</em>. Each acid has two H-bond acceptors — the N in the amino and the O in the carbonyl group.
“They have different numbers of carbon atoms” is <em>incorrec</em>t. They each contain six carbon atoms.
