Structure Determination: Mass Spectroscopy and Infrared Spectroscopy

Question:The mass spectrum (a) and the infrared spectrum (b) of an unknown hydrocarbon are shown. Propose as many structures as you can.

Question: The mass spectrum (a) and the infrared spectrum (b) of another unknown hydrocarbon are shown. Propose as many structures as you can.

Propose structures for compounds that meet the following descriptions:

1. An optically active compound C₅H₁₀O with an IR absorption at 1730 cm^-1 .
2.  A non-optically active compound C₅H₉N with an IR absorption at 2215 cm^-1 . 

Question: Propose structures for compounds that meet the following descriptions:

4-Methyl-2-pentanone and 3-methylpentanal are isomers. Explain how

you could tell them apart, both by mass spectrometry and by infrared

spectroscopy.

Question: 4-Methyl-2-pentanone and 3-methylpentanal are isomers. Explain how you could tell them apart, both by mass spectrometry and by infrared spectroscopy.

Grignard reagents undergo a general and very useful reaction with

ketones. Methylmagnesium bromide, for example, reacts with cyclohexanone to yield a product with the formula C₇H₁₄O . What is the structure of this product if it has an IR absorption at 3400 cm^-1 ?

Question: Grignard reagents undergo a general and very useful reaction with

ketones. Methylmagnesium bromide, for example, reacts with cyclohexanone  to yield a product with the formula ${\mathbf{C}}_{\mathbf{7}}{\mathbf{H}}_{\mathbf{14}}\mathbf{O}$ . What is the structure of this product if it has an IR absorption at $\mathbf{3400}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$?

Ketones undergo a reduction when treated with sodium borohydride, NaBH₄

 . What is the structure of the compound produced by reaction

of 2-butanone with NaBH₄  if it has an IR absorption at 3400 cm^-1 and M⁺ = 74 in the mass spectrum?

Question: Ketones undergo a reduction when treated with sodium borohydride, ${\mathbf{NaBH}}_{\mathbf{4}}$ .What is the structure of the compound produced by reaction of 2-butanone with ${\mathbf{NaBH}}_{\mathbf{4}}$  if it has an IR absorption at $\mathbf{3400}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{74}$ in the mass spectrum?

Nitriles, R - C = N , undergo a hydrolysis reaction when heated with

aqueous acid. What is the structure of the compound produced by hydrolysis of propanenitrile, CH₃CH₂C=N , if it has IR absorptions from 2500-3100cm^-1 and at 1710cm^-1 , and has M⁺ = 74?

Question: Nitriles,$\mathbf{R}\mathbf{-}\mathbf{C}\mathbf{\equiv }\mathbf{N}$ , undergo a hydrolysis reaction when heated with aqueous acid. What is the structure of the compound produced by hydrolysis of propanenitrile, ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\mathbf{\equiv }\mathbf{N}$ , if it has IR absorptions from $\mathbf{2500}\mathbf{-}\mathbf{3100}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and at $\mathbf{1710}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ , and has  ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{74}$?

The infrared spectrum of the compound with the mass spectrum shown below lacks any significant absorption above 3000cm^-1 . There is a prominent peak near 1740cm^-1  and another strong peak near 1200cm^-1  .

Propose a structure consistent with the data.

Question: The infrared spectrum of the compound with the mass spectrum shown below lacks any significant absorption above $\mathbf{3000}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ . There is a prominent peak near $\mathbf{1740}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and another strong peak near $\mathbf{1200}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ . Propose a structure consistent with the data.

The infrared spectrum of the compound with the mass spectrum shown below has a medium-intensity peak at about 1650cm^-1. There is also a

C-H out-of-plane bending peak near 880cm^-1 . Propose a structure consistent with the data.

Question: The infrared spectrum of the compound with the mass spectrum shown below has a medium-intensity peak at about $\mathbf{1650}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. There is also a C-H out-of-plane bending peak near $\mathbf{880}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ . Propose a structure consistent with the data.

The infrared spectrum of the compound with the mass spectrum shown below has strong absorbances at 1584, 1478, and 1446 cm^-1 . Propose a

structure consistent with the data.

Question: The infrared spectrum of the compound with the mass spectrum shown below has strong absorbances at 1584, 1478, and $\mathbf{1446}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ . Propose a structure consistent with the data.