Question

1. what is the lowest molar mass alkane that is chiral? draw stereochemical formulas of each enantiomer and specify which one is r or s. is there another alkane of the same molar mass that is also chiral? if so, draw its both enantiomers. hint: you can start with simple alkanes such as methane, ethane, and propane and determine whether they have any chiral carbons. you would need to look into branched alkanes to find chiral carbons. note alkanes contain carbons and hydrogens only, and there are neither carbon - carbon double or triple bonds nor ring structure in alkanes.

Explanation:

Step1: Analyze simple alkanes

Methane ($CH_4$), ethane ($C_2H_6$), propane ($C_3H_8$) have no chiral carbons. A chiral carbon has four different groups attached.

Step2: Consider branched alkanes

For alkanes, start with $C_7H_{16}$. The alkane 3 - methylhexane has a chiral carbon.
The formula for 3 - methylhexane is $CH_3CH_2CH(CH_3)CH_2CH_2CH_3$.
To assign $R/S$ configuration:

• First, assign priorities to the groups attached to the chiral carbon. Using the Cahn - Ingold - Prelog rules (higher atomic number gets higher priority). For the chiral carbon in 3 - methylhexane, the groups are: $-CH_2CH_3$ (priority 2), $-CH(CH_3)CH_2CH_2CH_3$ (priority 3), $-CH_3$ (priority 4), and the carbon chain continuation (priority 1).
• If the order of priority from 1 - 2 - 3 is clockwise with the lowest priority group (here $-CH_3$) pointing away, it is $R$. If counter - clockwise with the lowest priority group pointing away, it is $S$.

Another alkane of the same molar mass (same molecular formula $C_7H_{16}$) that is chiral is 2,3 - dimethylpentane. The formula is $CH_3CH(CH_3)CH(CH_3)CH_2CH_3$.

Answer:

The lowest molar mass chiral alkane is 3 - methylhexane.
For 3 - methylhexane:

• Enantiomer 1 (R - 3 - methylhexane): [Draw the stereochemical formula with the appropriate group orientations for R configuration]
• Enantiomer 2 (S - 3 - methylhexane): [Draw the stereochemical formula with the appropriate group orientations for S configuration]

Another chiral alkane of the same molar mass ($C_7H_{16}$) is 2,3 - dimethylpentane.

• Enantiomer 1 of 2,3 - dimethylpentane: [Draw its stereochemical formula]
• Enantiomer 2 of 2,3 - dimethylpentane: [Draw its stereochemical formula]