Sketch the following spectra that would be obtained for 2-chloroethanol: b. The 1H NMR spectrum for a sample of the alcohol that contains a trace amount of acid.

Ch. 14 - NMR Spectroscopy

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Bruice 8th Edition

Ch. 14 - NMR Spectroscopy

문제 69b

14장, 문제 69b

Sketch the following spectra that would be obtained for 2-chloroethanol:
b. The ¹H NMR spectrum for a sample of the alcohol that contains a trace amount of acid.

검증된 단계별 안내

Identify the structure of 2-chloroethanol (ClCH2CH2OH) and determine the types of protons present. There are three distinct types of protons: (1) the protons on the CH2 group attached to the chlorine atom, (2) the protons on the CH2 group attached to the hydroxyl group, and (3) the hydroxyl proton (OH).

Consider the effect of a trace amount of acid in the sample. The acid can cause rapid exchange of the hydroxyl proton (OH) with other protons in the solution, leading to broadening or disappearance of the OH signal in the 1H NMR spectrum.

Analyze the chemical shifts for the remaining protons: (1) The CH2 group attached to the electronegative chlorine atom will appear downfield (higher ppm) due to deshielding. (2) The CH2 group attached to the hydroxyl group will also be deshielded but to a lesser extent than the CH2 group attached to chlorine.

Determine the splitting patterns for each type of proton: (1) The CH2 group attached to chlorine will be split into a triplet due to coupling with the adjacent CH2 group (n+1 rule, where n = 2). (2) The CH2 group attached to the hydroxyl group will also be split into a triplet due to coupling with the adjacent CH2 group. The OH proton typically does not show splitting due to rapid exchange in the presence of acid.

Sketch the spectrum: (1) A triplet for the CH2 group attached to chlorine at a downfield position (higher ppm). (2) A triplet for the CH2 group attached to the hydroxyl group at a slightly upfield position (lower ppm compared to the first triplet). (3) The OH signal may be absent or appear as a broad peak depending on the exchange rate with the acid.

비슷한 문제에 대한 검증된 영상 답변:

이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

10m

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Nuclear Magnetic Resonance (NMR) Spectroscopy

NMR spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It relies on the magnetic properties of certain nuclei, such as hydrogen-1 (1H), to provide information about the environment of atoms within a molecule. In 1H NMR, the chemical shifts, splitting patterns, and integration of peaks reveal details about the number of hydrogen atoms and their connectivity.

Chemical Shifts

Chemical shifts in NMR spectroscopy refer to the resonance frequency of a nucleus relative to a standard reference, typically tetramethylsilane (TMS). They are measured in parts per million (ppm) and provide insight into the electronic environment surrounding the hydrogen atoms. For 2-chloroethanol, the presence of electronegative atoms like chlorine and oxygen will influence the chemical shifts, causing them to appear downfield (at higher ppm values).

Spin-Spin Coupling

Spin-spin coupling, or J-coupling, occurs when non-equivalent hydrogen atoms influence each other's magnetic environments, leading to splitting of NMR signals. This results in multiplet patterns that provide information about the number of neighboring hydrogen atoms. In the case of 2-chloroethanol, the splitting pattern will help identify the connectivity of the hydrogen atoms on the carbon chain, revealing the presence of adjacent protons.