What term describes the relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2R,3R,4R)-2,3,4-trichloroh

Question

a. enantiomers
b. not isomers
c. constitutional isomers
d. conformers
e. diastereomers

Answer 1

Because you don't give me the full name of the isomers, I cannot say which simmetry the molecules have.
With only partial names the most reasonable answer is
e. diastereoisomers
because you're are changing only 1 stereocenter.

Answer 2

e. diastereomers.

The easiest way to determine multiple stereocentres in a non-cyclic molecule is to draw it in a Fisher projection. In this the 2R,3R,4S stereoisomer is drawn as follows: Methyl group on top connected to a straight line, draw three bisecting lines on the straight line, then draw a propyl group at the bottom of the line. The bisecting lines are your groups of interest (C2, C3, and C4). The Cl's go on left, left and left (please make sure you know why), in the second structure; 2R,3R, 4R; the Cl's go on left, left and right. If you draw the structures next to each other you can see that they are not non-superimposable mirror images of each other and hence not enantiomers. By definitions, stereoisomers that are not enantiomers are diastereomers. The enantiomer would be the SSR stereoisomer (note the enantiomer of S is R, SS is RR, SR is RS, SSS is RRR, RRS is SSR, SSSS is RRRR etc)