Part 1: Select the multiplicity for the indicated proton signal.
Structure A methylene —Select— singlet doublet triplet quartet quintet sextet septet octet nonet decet
Structure B methyl —Select— singlet doublet triplet quartet quintet sextet septet octet nonet decet
Structure B methylene —Select— singlet doublet triplet quartet quintet sextet septet octet nonet decet
Structure C methyl —Select— singlet doublet triplet quartet quintet sextet septet octet nonet decet
Structure C methine —Select— singlet doublet triplet quartet quintet sextet septet octet nonet decet
Structure D methyl —Select— singlet doublet triplet quartet quintet sextet septet octet nonet decet
Structure D methylene —Select— singlet doublet triplet quartet quintet sextet septet octet nonet decet
Part 2: Give the integration ratio for the actual number of “different” hydrogens with the most downfield resonating proton listed first in the integration ratio. The sum of the numbers that make up the ratio should be the same as the number of hydrogens in the molecule.
(Input the ratio format using a colon to separate numbers like2:6)
Structure A
Structure B
Structure C
Structure D
Part 3: Give the number (write a number, not a word) of carbon signals that would appear in the13C NMR spectrum for
Structure A
Structure B
Structure C
Structure D
The Correct Answer and Explanation is :
To address your question on the given NMR problem, let’s break it down into three parts, as outlined in the task.
Part 1: Select the Multiplicity for the Indicated Proton Signal
In proton NMR, the multiplicity is determined by the ( n+1 ) rule, where ( n ) is the number of equivalent neighboring protons within 3 bonds. Each structure’s proton multiplicity depends on the neighboring proton count.
- Structure A (methylene): Likely a triplet, as it’s typically flanked by two hydrogens.
- Structure B (methyl): Likely a singlet, as a methyl group typically doesn’t have nearby non-equivalent protons.
- Structure B (methylene): Likely a quartet, if attached to a methyl group.
- Structure C (methyl): Likely a doublet, indicating it has one neighboring proton.
- Structure C (methine): Likely a multiplet or quartet, due to interaction with nearby protons.
- Structure D (methyl): Likely a triplet, if next to a methylene.
- Structure D (methylene): Likely a quartet, if next to a methyl group.
Part 2: Integration Ratio
The integration ratio reflects the relative number of hydrogens associated with each peak.
- Structure A: Assuming a single group, ( 2:2 ) (downfield hydrogens first).
- Structure B: May have a ratio like ( 3:2 ) or ( 3:1 ), depending on proximity of hydrogens.
- Structure C: Could show ( 3:1:1 ), reflecting methyl and methine groups.
- Structure D: Likely ( 6:2:2 ), indicating symmetrical methyl and methylene hydrogens.
Part 3: ( ^{13}C ) NMR Signals
Carbon NMR shows one peak per unique carbon environment.
- Structure A: Likely 2 unique carbons.
- Structure B: Likely 3 unique carbons.
- Structure C: Likely 3 or 4 unique carbons, depending on symmetry.
- Structure D: Likely 3 unique carbons.
Explanation (300 words):
The multiplicity of proton signals in ( ^1H ) NMR depends on coupling interactions between protons. Each set of protons splits based on the number of adjacent protons (( n+1 ) rule), producing singlets, doublets, triplets, and so on. For example, methyl groups adjacent to a single proton split into a doublet, while a methylene group surrounded by two hydrogens results in a triplet. Symmetry also plays a role in simplifying NMR spectra.
Integration ratios provide relative proton counts. Peaks integrate to reflect the number of hydrogens corresponding to each signal. For example, a methyl group integrates to three protons, while a methylene group integrates to two. The ratios must sum to the total number of hydrogens in the molecule and prioritize downfield signals.
Carbon NMR highlights unique carbon environments. Symmetry simplifies ( ^{13}C ) spectra as equivalent carbons overlap, reducing the number of distinct signals. For instance, a symmetrical molecule like isobutane would show fewer signals compared to a non-symmetrical molecule.
Correct interpretation of multiplicity, integration, and ( ^{13}C ) signals requires evaluating molecular structure, symmetry, and chemical environment to accurately identify peaks and assign values.