Question

Label the significant peaks in the IR and NMR spectra. When analyzing the signals in the 'H NMR, be sure to include all appropriate information. For example: 3H, singlet, 0 neighbors, and c (the letter referring to the corresponding unique type of hydrogens that were labeled in the structure). It is recommended to provide more analysis for each signal than what is described above, when necessary, such as labeling any coupling constants if any are provided. For c NMR label each peak to the corresponding carbon in your sugsested structure. The following IR and NMR spectra are of a compound with the molecular formula of CsHe. Draw the correct structure

thank you in advance

Answer 1

IR Spectrum

3308cm-1 - strong peak due to alkyne C-H stretching

2966cm-1, 2937cm-1, 2876cm-1 - alkyl C-H streching

2128cm-1 - medium, alkyne C $\equiv$ C stretching

1480cm-1, 1381cm-1 - alkyl C-H bending

1277cm-1 -  $\equiv$ C-H bending

NMR Spectrum

the molecular formula of the compound is given as C₅H_8, and the 13C-NMR consists of 5 different signal suggest that all the 5 carbons have a different environment. The proposed structure is 1-Pentyne

CH₃-CH₂-CH₂-C$\equiv$C-H

H-NMR

i. 2.2ppm - 2H, triplet of doublets, 3 neighbors [2 (CH2) +1 ($\equiv$CH)], b. CH2 hydrogens b, is split by the hydrogens across the triple bond, even though it is separated from them by three carbons.

ii. 1.9ppm - 1H, triplet, 2 neighbors, a. the terminal hydrogen is split by the hydrogens across the triple bond, even though it is separated from them by three carbons.

iii. 1.6ppm - 2H, sextet, 5 neighbors, c

iv. 1.12ppm - 3H, triplet, 2 neighbors, d

13-C-NMR

Cdoaw c b d e.

i. 84ppm - Cb

ii. 68ppm - Ca

iii. 21.8ppm - Cc

iv. 20.2ppm - Cd

v. 13.0ppm - Ce