Stereochemistry

What is the relationship between the compounds?

• unrelated

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Choose the compound that is a constitutional isomer of this compound:

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What is the relationship between the compounds:

(3S,4R)-4-methylheptan-3-ol

and

(3R,5S)-5-methylheptan-3-ol

• unrelated

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Answer explanation

Careful, they are connected differently. The chiral centers are at different carbons (3,4) and (3,5), so they are not configurational isomers (enantiomers or diastereomers). Do not be fooled by the R and S tags in the name. If they are at different numbers on the chain as they are, cannot be enantiomers.

What is the relationship between the compounds:

(3S,5R,8S)-8-chloro-5-methyldecan-3-ol

and

(3R,5S,8S)-8-chloro-5-methyldecan-3-ol

• unrelated

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Answer explanation

The compound names including locants (#s) are the same, so they have the same formula and are connected the same. The difference is in the configuration of the chiral centers. In the second compound, two are switched but the third is the same. Diastereomer.

What is the relationship between the compounds?

• same compound

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Answer explanation

The structure on the left has a line of symmetry going diagonally through unsubstituted cyclobutane carbons, with cis methyls on the other carbons, so it is achiral. No enantiomer exists. The structure on the left also has cis methyls at the 1 and 3 carbons. It has the same relative configuration (cis) so must be the same compound. Turn it over left to right and you'll see it is the same.

Tags

NGSS.HS-PS1-2

What is the relationship between the compounds?

• unrelated

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Answer explanation

The compounds are connected the same (front and back carbons have same groups). One is staggered and the other eclipsed which is a difference in 3D space, and rotating the bonds resolves this difference. They are conformational isomers. (The back carbon is a C with three H, so there is no chiral center in this compound. It is achiral)

What is the relationship between the compounds?

• unrelated

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Answer explanation

The compounds are connected differently. The front carbons of the Newman projections are attached to different groups. If you look carefully, they do indeed have the same formula so they are constitutional isomers.

Tags

NGSS.HS-PS1-3

What is the relationship between the compounds?

• same compound

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Answer explanation

The compounds have the same formula and connectivity. The question is whether there is some 3D difference and if so, these are mirror images. You cannot slide one over the other and get the groups to superimpose, so they are not the same compound. If you turn one over left-right, you'll see they are mirror images. (or, recognize that the bold/dash groups on each chiral center are switched at each chiral center, so yes, mirror images)

What is the relationship between the compounds?

• same compound

• enantiomers

• diastereomers

• conformational isomers

• constitutional isomers

Answer explanation

The compounds have the same formula and connectivity, but there is some 3D difference. The relative configuration of the chiral centers is not preserved comparing one to the other (syn/anti). They cannot be enantiomers. They are diastereomers.

Assume all you know about a compound is that the name is (+)-d-glucose and select all true statements. (i.e., do NOT look up information about the structure. Use the name only.)

• It is chiral.

• It has one chiral center.

• The enantiomer rotates plane-polarized light counterclockwise.

• It has three diastereomers.

• It rotates plane-polarized light clockwise.

Answer explanation

The + indicates that this compound rotates plane-polarized light clockwise. It must be chiral, since only chiral compounds rotate plane-polarized light. The enantiomer will rotate light in the opposite direction, counterclockwise with a - symbol in front of the name. You do not know anything about the structure including the number of chiral centers, so you have no idea how many diastereomers are possible.