Question

Give the structure that corresponds to the following molecular formula, reaction data, and ^1H NMR spectrum: This compound undergoes catalytic hydrogenation to give 2,2,4-trimethylpentane.The magenta numbers in the spectrum are the relative integrals in arbitrary units, and the violet numbers are coupling constants.Give the structure that corresponds to the following molecular formula, reaction data, and 1H NMR spectrum: This compound undergoes catalytic hydrogenation to give 2,2,4-trimethylpentane.

Give the structure that corresponds to the following molecular formula, reaction data, and 1H NMR spectrum: This compound undergoes catalytic hydrogenation to give 2,2,4-trimethylpentane.

Answer 1

Concepts and reason

The $^1{\rm{H}}$ NMR spectrum of a compound with molecular formula ${{\rm{C}}_8}{{\rm{H}}_{16}}$ is given and the structure needs to be given. Calculate the double bond equivalent and then find the magnetically equivalent protons based on the splitting of the peaks and verify whether the given structure gives exactly the same peaks from the given NMR figure.

Fundamentals

The NMR spectrum is used for identification of compounds based on the nature of hydrogens or carbons present in an organic compound. Two types of NMR spectrum are there - $^1{\rm{H}}$ and $^{13}{\rm{C}}$ . It identifies the chemical environment of the hydrogens and carbons based on the spectrum taken which helps in identifying a compound.

The frequency of a nuclei is measured with respect to a standard in a magnetic field known as chemical shift. The standard used in NMR is tetramethyl silane (TMS).

The inductive effect plays a crucial role in the NMR spectrum. In case of presence of an electron withdrawing substituent, the electron density shifts towards the electronegative element and hence, the signal appears downfield whereas if the proton is attached with an electron releasing substituent, the signal appears upfield.

The protons or carbons give different peak based on the chemical environment they are present in and give a single peak if they are present in same chemical environment.

Magnetically equivalent protons are the protons that give the same peaks. These protons on replacement with another substituent give the same compound.

The spin-spin coupling is another feature of NMR spectrum that helps in identification of structure. Protons present in different chemical environments lead to the splitting of a NMR peak. The number of peaks obtained are given as n+1 where n is the number of equivalent protons.

Thus, the peaks obtained are singlet, doublet, triplets, quartets based on n = 0, 1, 2, 3 and so on respectively.

The integration value or the area under the peak corresponds to the protons that give rise to a particular NMR signal.

The double bond equivalent of the given compound is one.

The alkene molecules on hydrogenation gives 2,2,4-trimethylpentane as follows:

The structure of the alkene is as follows:

Ans:

The structure of the given spectrum is as follows: