There are nine constitutional isomers of molecular formula C7H16. 1)

There are nine constitutional isomers of molecular formula C7H16. 1) What is the unsaturation number of each of these compounds? 2) Draw five constitutional isomers, where two of these are chiral compounds. 3) For the three achiral constitutional isomers, provide the correct IUPAC names.
There are nine constitutional isomers of molecular formula C7H16.

1) What is the unsaturation number of each of these compounds?ÂÂ

2) Draw five constitutional isomers, where two of these are chiral compounds.ÂÂ

3) For the three achiral constitutional isomers, provide the correct IUPAC names.ÂÂ

4) For the two chiral constitutional isomers, draw in Fischer projection formula the enantiomers of each.

5) Name, according to IUPAC standards, each of the enantiomers you drew in #4 above.ÂÂ

The Correct Answer and Explanation is :

Let’s go through each part of the problem systematically.

1) Unsaturation Number of Each Compound

The molecular formula C7H16 represents an alkane, which has no double or triple bonds. The unsaturation number (also known as the index of hydrogen deficiency, IHD) is a measure of the number of rings and/or double bonds in a molecule.

For a saturated compound, the formula would be CₙH₂ₙ₊₂ (where “n” is the number of carbon atoms). For C7H16, the saturated formula is C7H16, so there are no rings or double bonds. This means the unsaturation number for the compound is 0.

Even for the constitutional isomers, this unsaturation number remains 0 since all of them are saturated (alkanes or branched alkanes).

2) Draw Five Constitutional Isomers, Including Two Chiral Compounds

The five constitutional isomers of C7H16 can be represented as:

1. Heptane (n-heptane): Straight-chain with no branching.
2. 2-Methylhexane: A six-carbon chain with a methyl group attached to the second carbon.
3. 3-Methylhexane: A six-carbon chain with a methyl group attached to the third carbon.
4. 2,2-Dimethylpentane: A five-carbon chain with two methyl groups attached to the second carbon.
5. 2,3-Dimethylpentane: A five-carbon chain with one methyl group on the second carbon and another on the third carbon.

Chirality:

• 2-Methylhexane and 3-Methylhexane are not chiral because they have symmetrical structures.
• 2,2-Dimethylpentane and 2,3-Dimethylpentane can be chiral if the substituents lead to non-superimposable mirror images, especially if asymmetry arises at the points of branching.

3) IUPAC Names for Three Achiral Isomers

The three achiral isomers of C7H16 (no chiral centers):

1. Heptane (n-heptane)
2. 2-Methylhexane
3. 3-Methylhexane

These are the linear and branched structures with no chiral centers.

4) Fischer Projection of Enantiomers for Two Chiral Compounds

To visualize the enantiomers, we need to identify compounds that have chiral centers. For example:

• 2,3-Dimethylpentane: The chiral centers are at carbons 2 and 3.
• 2,2-Dimethylpentane: The chiral centers are at carbon 2.

Fischer Projections can be drawn for both pairs of enantiomers. Each enantiomer will have opposite configurations (R/S) at the chiral centers.

5) IUPAC Names for Enantiomers

For the 2,3-dimethylpentane enantiomers, the IUPAC names would be:

1. (R)-2,3-dimethylpentane
2. (S)-2,3-dimethylpentane

Similarly, for the 2,2-dimethylpentane enantiomers:

1. (R)-2,2-dimethylpentane
2. (S)-2,2-dimethylpentane

Conclusion

• Unsaturation Number: All isomers have an unsaturation number of 0 (since they are saturated).
• Chirality: 2,2-Dimethylpentane and 2,3-Dimethylpentane can be chiral compounds, and their enantiomers will have opposite configurations (R/S).
• IUPAC Names: For the achiral isomers, the names are n-heptane, 2-methylhexane, and 3-methylhexane.

This provides a comprehensive overview of the constitutional isomers and chirality of C7H16 compounds.