Chapter 10.2, Problem 14E

(a)

Interpretation Introduction

Interpretation: To specify the absorptions which are associated with the carbon-carbon double bond and the hydrogen linked with the first carbon atom.

Concept Introduction: The spectroscopy which includes the interaction of infrared radiation with matter is known as IR spectroscopy. It comprises various techniques, related to absorption spectroscopy. IR spectroscopy is also used to study and recognizing chemical substances.

Answer to Problem 14E

Absorptions associated with the carbon-carbon double bond and the hydrogen linked with C1 carbon atom of 2-methyl -1-butene is as follows:

Wave number	Type of bond
$\sim 1500{\text{cm}}^{-1}$	$\text{C=C}$ stretching
$\sim 3000{\text{cm}}^{-1}$	$\text{C=C}-\text{H}$ stretching

Explanation of Solution

The structure of 2-methyl -1-butene is as follows:

  

Important IR stretching frequencies are as follows:

Wave number   $\left({\text{cm}}^{-}\right)$	Type of bond
$\text{C=C}$	$1680-1600$
$\text{C=N}$	$1650-1550$
$\text{C=O}$	$1780-1650$
$\text{C}-\text{O}$	$1250-1050$
$\text{C}-\text{H}$	$3300-2700$
$\text{O}-\text{H}$ (alcohol)	$3650-3200$
$\text{O}-\text{H}$ (carboxylic acid)	$3300-2500$
	$2260-2220$
	$\text{226}0-\text{21}00$
$\text{N}-\text{H}$	$3500-3300$
	$\sim 1600\text{and }\sim \text{1500}-1430$

From the given spectral data of 2-methyl -1-butene, absorptions associated with the $\text{C=C}$ double bond and the hydrogen attached to the C1 carbon atom is as follows:

Wave number	Type of bond
$\sim 1500{\text{cm}}^{-1}$	$\text{C=C}$ stretching
$\sim 3000{\text{cm}}^{-1}$	$\text{C=C}-\text{H}$ stretching

(b)

Interpretation Introduction

Interpretation: To assign the various resonances to the hydrogen nuclei of 2-methyl -1-butene in ${}^1\text{H}$ NMR spectrum.

Concept Introduction: Nuclear magnetic resonance (NMR) is a spectroscopy technique that works on the basis that the nucleus of the atoms absorbs electromagnetic radiation in the radio frequency region.

  ${}^1\text{H}\text{NMR}$ or proton nuclear magnetic resonance is a tool for explaining the number of protons or hydrogen in the compound.

Answer to Problem 14E

Assignment of ${}^1\text{H}$ NMR of 2-methyl -1-butene is as follows:

  

Explanation of Solution

From the given NMR data of 2-methyl -1-butene, assignment of ${}^1\text{H}$ NMR of 2-bromo-2methylbutane is as follows:

  

Main features of ${}^1\text{H}$ NMR of 2-methyl -1-butene are as follows:

1. The methyl protons ( ${\text{CH}}_3-$ ) give rise to a signal at $\text{δ 1}\text{.75}$ as a 3H, singlet as protons are allylic and no adjacent protons are present.
2. The vinylic proton $={\text{CH}}_{\text{2}}$ gives signal of 2H at $\text{δ 4}\text{.80}$ .
3. The allylic protons ( $-{\text{CH}}_{\text{2}}-$ ) gives a quartet signal at $\text{δ 2}\text{.00}$ .
4. The terminal protons in ( $-{\text{CH}}_3$ ) gives peak around at $\text{δ 1}\text{.05}$

(c)

Interpretation Introduction

Interpretation: To assign the various resonances to the hydrogen nuclei of 2-methyl -1-butene in ${}^{13}\text{C}$ NMR spectrum.

Concept Introduction: Carbon-13 NMR has several merits over proton NMR in terms of its power to explain biochemical and organic structures. Carbon-13 NMR provides information related to the backbone of molecules instead of the periphery. In addition, the chemical shift range for Carbon-13 for most organic compounds is around 200 ppm related with 10 to 15 ppm for the proton.

Answer to Problem 14E

The assignment of ${}^{13}\text{C}$ NMR of 2-methyl -1-butene is as follows:

  

Explanation of Solution

The range of chemical shift in ${}^{13}\text{C}$ NMR spectra are-

Structure	Chemical shift (ppm)
${\text{RCH}}_{\text{2}}\text{OH}$	$50-65$
${\text{RCH}}_{\text{2}}\text{R}$	$15-55$
${\text{RCH}}_3$	$10-40$
${\text{R}}_3\text{CH}$	$20-60$
$\text{C=C}$	120-140

From the given NMR data of 2-methyl -1-butene, the assignment of ${}^{13}\text{C}$ NMR of 2-methyl -1-butene is as follows: