How many chiral carbons are in the following semi-structural formula?CH3CH2CHClCHOHCH3单项选择题
A
a. 1
B
b. 2
C
c. 3
D
d. 4

Question

How many chiral carbons are in the following semi-structural formula?CH3CH2CHClCHOHCH3

BlackTom AI · Accepted Answer

The question asks us to determine how many chiral centers are present in the given semi-structural formula: CH3CH2CHClCHOHCH3.

Option a. 1: This would be true if only one carbon in the chain had four distinct substituents. However, we need to examine each potential stereocenter carefully before concluding.

Option b. 2: This is plausible because two different carbons may each be bonded to four different groups, creating two stereocenters. Specifically, consider the carbon labeled as CHCl (the third carbon from the left): it is attached to H, Cl, the ethyl group (CH2CH3), and the remaining fragment (CHOHCH3). All four substituents are distinct, so this carbon is a stereocenter. Next, look at the carbon labeled as CHOH (the fourth carbon): it is bonded to OH, H, a CH3 group, and the previous carbon (CHCl-...), which are all different, making this carbon also a stereocenter.

Option c. 3: To reach three chiral centers, there would need to be three carbons with four distinct substituents. In this molecule, only two carbons meet the criterion described above; the remaining carbons (terminal CH3, CH2, and possibly others) do not have four different substituents.

Option d. 4: This would require all four carbons in the chain to be stereocenters. In this structure, the terminal methyl carbon (CH3) and the second carbon (CH2) are not chiral, since they have at least one pair of identical substituents or insufficient connectivity for four distinct groups.

To recap the reasoning: the third carbon (the one bearing Cl) has four different substituents (H, Cl, ethyl group, and the rest of the chain), making it chiral. The fourth carbon (the one bearing OH) also has four different substituents (OH, H, methyl group, and the preceding carbon fragment), making it chiral as well. Therefore, there are two chiral centers in total, and option b is correct. The other options miscount or misclassify the chirality of one or both of these centers.

How many chiral carbons are in the following semi-structural formula?CH3CH2CHClCHOHCH3单项选择题

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