Q53E - Organic Chemistry (Mcmurry)

Question

The red fox (Vulpesvulpes) uses a chemical communication system based on scent marks in urine. One component of fox urine is a sulfide whose mass spectrum has ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{116}$. IR spectroscopy shows an intense band at $\mathbf{890}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$and ${}^{\mathbf{1}}\mathbf{H}$NMR spectroscopy reveals the following peaks:

$\mathbf{1}\mathbf{.74}\mathbf{\delta }$ ($\mathbf{3}\mathbf{H}$, singlet); $\mathbf{2}\mathbf{.11}\mathbf{\delta }$($\mathbf{3}\mathbf{H}$, singlet); $\mathbf{2}\mathbf{.27}\mathbf{\delta }$($\mathbf{2}\mathbf{H}$, triplet, $\mathbf{J}\mathbf{=}\mathbf{4}\mathbf{.2}\mathbf{Hz}$); $\mathbf{2}\mathbf{.57}\mathbf{\delta }$($\mathbf{2}\mathbf{H}$, triplet$\mathbf{J}\mathbf{=}\mathbf{4}\mathbf{.2}\mathbf{Hz}$, ); $\mathbf{4}\mathbf{.73}\mathbf{\delta }$($\mathbf{2}\mathbf{H}$, broad). Propose a structure consistent with these data. [Note:${\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}\mathbf{S}$ absorbs at $\mathbf{2}\mathbf{.1}\mathbf{\delta }$].

Step-by-Step Solution

Answer

The structure corresponding to these data is given below

The structure given above is of sulfide, and ${\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}\mathbf{S}$ group absorbs at $\mathbf{2}\mathbf{.1}\mathbf{\delta }$ .

Step 1: Theoretical values of IR absorption and mass spectrum

Mass spectrum ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{116}$denotes the molecular mass of the compound. It also explains the degree of saturation or unsaturation. IR absorption at $\mathbf{890}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ denotes the alkene group in the compound.

Step 2: Observation from IR absorption band

IR spectroscopy has an intense band at $890{\mathrm{cm}}^{-1}$ . This means that one degree of unsaturation or an alkene group is present. 

Step 3: Observation of mass spectrum

Mass spectrum tells that ${\mathrm{M}}^{+}=116$. It denotes the molecular mass of the compound is $116$ and has a sulfide group, i.e., the compound has the molecular formula ${\mathrm{C}}_6{\mathrm{H}}_{12}\mathrm{S}$ .

Molecular mass $\mathrm{M}=(12\times 6)+(12\times 1)+32=116$

Step 4: Observation from H 1 NMR spectroscopy

Each chemical shift is denoted by a, b, c, d, and e..$\mathrm{a}=1.74\mathrm{\delta },\mathrm{b}=2.11\mathrm{\delta },\mathrm{c}=2.27\mathrm{\delta },\mathrm{d}=2.57\mathrm{\delta },\mathrm{e}=4.73\mathrm{\delta }$ ‘a’ has single peak with  three hydrogen atoms. This denotes that corresponding carbon atom has three hydrogen, and the neighboring carbon atom has no hydrogen. Similarly, ‘b’ has three hydrogen, and the neighboring carbon atom has no hydrogen. ‘c’ has two hydrogen atoms, and the neighboring carbon atom has two hydrogen atoms. ‘d’ is similar to ‘c.’ ‘e’ has two hydrogen atoms and is a broad peak.

The structure is as given below

Types of H in desired structure

Step 5: Proposed structure

The structure formed is given below.

Structure of unknown

The given structure is an alkene with a sulfur atom. The parent has four carbon atoms, hence the name but-1-ene.