Which structures represent R-3-methylhexane?
Help: Build the structures using a molecular model.

Question

Quizplus · Accepted Answer

R-3-methylhexane has a methyl group attached to the third carbon atom (the one in the middle of the chain), so structures I and III are potential candidates. The molecule is chiral, meaning that it is not superimposable on its mirror image, so we need to make sure that we are looking at two different arrangements of atoms. Structures II and IV are mirror images of each other, so they are not both R-3-methylhexane. Structure III is R-3-methylhexane because the three lowest priority substituents (i.e. the ones attached to C-2, C-4, and C-5) are in a counterclockwise direction when viewed along the C-3 to C-4 bond. Structure IV is also R-3-methylhexane because the lowest priority substituents are in a clockwise direction when viewed along the C-3 to C-4 bond. Therefore, the correct answer is A, structures III and IV represent R-3-methylhexane.

Which Structures Represent R-3-Methylhexane