Which region in the IR spectrum could be used to distinguish between the following structures?

Question

BlackTom AI · Accepted Answer

Amide C=O stretches appear in the mid-IR near 1630–1700 cm^-1 (the amide I band), so the presence of a CONH2 group versus a CH2NH2 group is best distinguished in the 1600–1650 cm^-1 region.

1) Relevant knowledge points and concepts
- Functional groups give characteristic IR absorptions: a carbonyl (C=O) in an amide gives a strong amide I band (~1630–1690 cm^-1, often ~1650 cm^-1 for conjugated/aromatic amides). 
- Primary amines (NH2) show N–H stretches around 3300–3500 cm^-1 and N–H bends near 1600–1650 cm^-1 can be weaker, but a strong, sharp C=O stretch is diagnostic for an amide.
- Alkyl/aromatic C–H stretches are 2850–3100 cm^-1 and C–C aromatic stretches appear around 1450–1600 cm^-1.

2) Step-by-step reasoning
- Identify the two structures: (A) benzamide (Ar–C(=O)–NH2) contains a carbonyl directly attached to an aromatic ring; (B) benzylamine (Ar–CH2–NH2) lacks a carbonyl and instead has a methylene next to an amine.
- The key differentiator is the presence vs absence of the C=O group. The strongest, most diagnostic band for that is the amide C=O stretch (amide I) near 1650 cm^-1.
- Therefore the IR region around 1600–1650 cm^-1 will show a strong C=O absorption for benzamide and no comparable C=O band for benzylamine.

3) (Calculations) No numeric calculation required; mapping of typical band positions suffices.

4) Why the correct answer is correct
- Option d (1600–1650 cm^-1) corresponds to the amide C=O stretch region; benzamide gives a strong band here while benzylamine does not. This provides a clear distinguishing feature.

5) Why other options are incorrect (brief)
- a (2850–3000 cm^-1): both compounds have C–H stretches in this region (aromatic and CH2), so not distinguishing.
- b (1800–1950 cm^-1): corresponds to highly conjugated/strained carbonyls or cumulenes (e.g., acid chlorides, anhydrides) not relevant here.
- c (1450–1550 cm^-1): falls in CH bending/aromatic ring region; both compounds show bands here and it won’t uniquely identify the carbonyl.

6) Conclusion
- The distinguishing IR region is 1600–1650 cm^-1, confirming answer d.

Which region in the IR spectrum could be used to distinguish between the following structures?Single choice

Similar Questions

Which functional group has a characteristic absorption in the 1630-1800 cm-1 region?

Which functional group has a characteristic absorption in the 1630-1800 cm-1 region?

Neither N 2 N 2 nor O 2 O 2 are greenhouse gases because BlackTom题目解析

Q11 V2The infrared spectrum of cocaine is shown below. From this spectrum it may be concluded that

Q11 V2The infrared spectrum of cocaine is shown below. From this spectrum it may be concluded that

Which one of the following compounds (1 to 4) corresponds to the IR spectrum shown? (you can refer to a table of characteristic absorptions) Spectra reproduced with permission from NIST

Which one of the following compounds (1 to 4) corresponds to the IR spectrum shown? (you can refer to a table of characteristic absorptions) Spectra reproduced with permission from NIST

Which one of the following compounds (1 to 4) corresponds to the IR spectrum shown? (you can refer to a table of characteristic absorptions) Spectra reproduced with permission from NIST

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler