Question

Identify product A from the given 1H NMR data. Treatment of CH2═CHCOCH3 with one equivalent of HCl forms compound A. A exhibits the following absorptions in its 1H NMR spectrum: 2.2 (singlet, 3 H), 3.05 (triplet, 2 H), and 3.6 (triplet, 2 H) ppm. What is the structure of A? Click the "draw structure" button to activate the drawing utility.

Answer 1

Answer:Please refer the attachment for the structure. The name of the compound is 4-chloro butan-2-one

Explanation:

When we treat CH₂=CHCOCH₃ with one equivalent of HCl , the alkene reacts with HCl to undergo  electrophilic addition to the C=C pi bond . The reaction is similar to Markowinkoffs addition reaction. The reaction leads to the formation of Cl-CH₂-CH₂-COCH₃ .

Kindly refer the attachment for mechanism of the reaction.

We can ascertain the structure of A from the NMR data available :

The NMR spectra has a absorption signal at 2.2 which can be ascertained to the CH₃(referred as 3 in structure protons)  group attached next to the  the carbonyl group as these protons generally appear at around 2.0-2.5ppm. These protons are slightly downfield as they are attached next to sp² hybridized carbonyl carbon. The spin multiplicity shown  by these protons is singlet which also shows that no coupling occurs as there are no available protons at  the neighboring carbonyl carbon.  

The NMR spectra has a absorption signal at 3.05  and it can  be ascertained  to CH₂ group  next to carbonyl group (referred as 2 in the structure). The protons appear slightly downfield due to carbonyl group and weak electron withdrawing inductive  effect of chlorine atom. The spin multiplicity of these protons is triplet on account of coupling with the neighboring CH₂ protons next to Cl.

The NMR spectra has a absorption signal at 3.79  and it can  be ascertained  to CH₂ group  next to chlorine group (referred as 1 in the structure). The protons appear slightly more  downfield due to strong electron withdrawing inductive effect of Cl atom. The spin multiplicity of these protons is triplet on account of coupling with the neighboring CH₂ protons next to carbonyl group.

Kindly refer attachment for reaction mechanism and structure.