Question

Predict the splitting pattern for each kind of hydrogen in isopropyl propanoate, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\).

Short answer

The splitting patterns are: doublet, septet, quartet, and triplet.

Step-by-step solution

Identify Types of Hydrogens

Begin by identifying the unique types of hydrogen atoms in isopropyl propanoate. In this molecule, you can find three types of hydrogens: those in the methyl groups ( (CH₃) ), those in the central methine group ( CH ), and those in the ethyl side chain ( CH₂CH₃ ).

Determine Neighboring Hydrogens

Determine the number of hydrogen atoms adjacent to each type of hydrogen to understand splitting patterns. For the methyl group on the isopropyl part, there are 1 neighbor hydrogen from the methine carbon; for the methine hydrogen, there are 6 neighboring hydrogens from both methyl groups; for the ethyl chain methyl hydrogens, there are 2 neighbors from the adjacent methylene group; and for the methylene hydrogens, 3 neighbors from the methyl group.

Predict the Splitting Patterns

Use the n+1 rule for NMR splitting to predict the splitting pattern: - Methyl hydrogens ( CH₃ ) on isopropyl: have one methine hydrogen as a neighbor, leading to a doublet pattern (2 peaks). - Methine hydrogen ( CH ): neighbors with six hydrogens (two CH₃ groups), resulting in a septet (7 peaks). - Methylene hydrogens ( CH₂ ) on ethyl: have three neighbors (methyl group), producing a quartet (4 peaks). - Methyl hydrogens ( CH₃ ) on ethyl: have two methylene hydrogens as neighboring, resulting in a triplet (3 peaks).

Key concepts

Isopropyl Propanoate

Isopropyl Propanoate is an organic compound that serves as an ester. Esters, in organic chemistry, are characterized by the functional group \(-\mathrm{COO}\-\). Isopropyl propanoate is specifically made from the reaction between propanoic acid and isopropyl alcohol. This compound is structured as follows: \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CO}_{2}\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\). In this structure:

• Isopropyl refers to the group attached to the ester oxygen (\(-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\)).
• Propanoate denotes the carbon chain derived from propanoic acid \(-\mathrm{CH}_2\mathrm{CH}_3\).

Understanding this compound helps in predicting how its hydrogen atoms will behave in NMR (Nuclear Magnetic Resonance) spectroscopy.

Hydrogen Types

In isopropyl propanoate, different hydrogen environments lead to distinct signals in an NMR spectrum. You can identify three main types of hydrogens:

• Methyl Hydrogens (\(\mathrm{CH}_3\)): Found at both ends of the molecule, contributing to the methyl groups in the isopropyl and ethyl portions. These hydrogens usually face slightly different environments due to their unique neighbors.


• Methine Hydrogen (\(\mathrm{CH}\)): Located at the center of the isopropyl group, this hydrogen is surrounded by other carbons, making it sensitive to different neighboring environments.


• Methylene Hydrogens (\(\mathrm{CH}_2\)): Part of the ethyl moiety \( \mathrm{-CH}_2\mathrm{CH}_3 \), these hydrogens experience interaction with adjacent methyl groups.

Different neighboring environments lead to different splitting patterns in NMR, which is a key consideration in measuring molecular structure.

N+1 Rule

The N+1 Rule in NMR spectroscopy is crucial for predicting the splitting pattern of hydrogen signals. The basic principle states that the number of peaks observed in the NMR spectrum is equal to the number of neighboring hydrogen atoms ( ) plus one. Let's review the splitting patterns for isopropyl propanoate:

• The isopropyl methyl hydrogens see one neighboring methine hydrogen, producing a doublet (2 peaks).


• The methine hydrogen is neighbors with six methyl hydrogens from both isopropyl methyl groups, resulting in a complex septet (7 peaks).


• The methylene hydrogens in the ethyl chain neighbor three methyl hydrogens, forming a quartet (4 peaks).


• The ethyl methyl hydrogens have two methylene neighbors, yielding a triplet (3 peaks).

This rule provides a clear prediction of signal multiplicity in NMR spectra, essential for interpreting results.

Methylene and Methyl Groups

Methylene (\(\mathrm{CH}_2\)) and methyl (\(\mathrm{CH}_3\)) groups are fundamental building blocks in organic molecules and play central roles in determining the NMR spectral features.

• Methyl Groups (\(\mathrm{CH}_3\)): Consist of three hydrogen atoms bonded to a single carbon. These groups are prevalent in organic compounds and produce specific signals in NMR due to their relative position in a molecule.


• Methylene Groups (\(\mathrm{CH}_2\)): Contain two hydrogen atoms bonded to a carbon. This distinct arrangement makes them sensitive to neighboring group interactions. In the case of isopropyl propanoate, methylene hydrogens typically split into a quartet due to their interactions with methyl groups.

Understanding these groups ensures effective analysis and identification of molecules using NMR, allowing chemists to deduce precise molecular structures.