How many constitutional isomers are possible for the formula C₆H₁₄?

Question

Quizplus · Accepted Answer

This formula represents a peptide chain with 5 amino acid residues. Constitutional isomers are formed by varying the sequence of the amino acid residues. There are 5 different amino acids that can be used and they can be arranged in any order, giving us 5! = 120 possible arrangements. However, since the amino acids cysteine (C) and histidine (H) have a side chain that can form disulfide bonds and coordination bonds, respectively, there are additional constraints on the possible arrangements. Specifically, the two cysteine residues can form a disulfide bond between them, which eliminates two constitutional isomers, and the histidine residue can coordinate with a metal ion, which eliminates another two constitutional isomers. Therefore, the total number of possible constitutional isomers is 120 - 2 - 2 = 116, which is closest to answer choice D (5).

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How Many Constitutional Isomers Are Possible for the Formula C₆H₁₄