Question

An organic compound absorbs strongly in the IR at 1687 cm1. Its 'H NMR spectrum consists of two signals, a singlet at 2.1 ppm and a multiplet centered at 7.1 ppm. Its mass spectrum shows significant peaks at m/z 120, m/z 105, m/z 77, and m/z 43. This information is consistent with which of the following structures? IV Propose structures for the ions with m/z values of 120, 105,77 and 43 obtained in the mass spectrum of the compound you selected.

Answer 1

This question does not contain the structures of the molecules. The structures in Daylight SMILES format are:

I. C1=CC=CC=C1C(=O)C

II. C1=CC=CC=C1CC=O

III. C1=CC(C)=CC=C1C=O

IV. C1=CC=CC=C1CCC

V. C1=CC=CC=C1C(C)C

The structures are also attached

Answer:

The structure of compound IV is consistent with the information obtained analysis

Proposed structures for the ions with m/z values of 120, 105,77 and 43 are (also attached):

C1=CC=CC=C1C(=[OH0+])C |^1:7|

C1C([CH0+]=O)=CC=CC=1

C1[CH0+]=CC=CC=1

C(#[OH0+])C

respectively

Explanation:

The IR peak at 1687 cm⁻¹ is indicative of an α unsaturated carbonyl carbon. While the 1H NMR singlet is of the methyl group next to carbonyl and the multiplet near 7.1 ppm is a characteristic peak of benzene. This data shows points towards structure I.

Mass spectrum peak at 120 m/z is of molecular ion peak. In the case of carbonyl-containing molecule, this peak is observable. The signal at 105 shows the loss of a methyl group next to the carbonyl. m/z value of 77 is the characteristic cationic peak of benzene, while the peak at 43 infers the formation of acylium ion (RCO+) due to α-cleavage. All this data agrees with the structure of acetophenone (Structure 1)