Question

\- The red fox (Vulpes vulpes) uses a chemical communication system based on scent marks in urine. One component of fox urine is a sulfide. Mass spectral analysis of the pure scent-mark component shows \(\mathrm{M}^{+}=\) 116 , IR spectroscopy shows an intense band at \(890 \mathrm{~cm}^{-1}\), and \({ }^{1}\) H NMR spectroscopy reveals the following peaks. Propose a structure for the molecule. [Note: \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~S}\) absorbs at \(\left.2.1 \delta .\right]\) \(1.74 \delta\) (3 H, singlet); \(2.11 \delta\) (3 H, singlet); \(2.27 \delta\) ( \(2 \mathrm{H}\), triplet, \(J=4.2 \mathrm{~Hz}\) );

Short answer

The structure is ethyl methyl sulfide (\(CH_3SCH_2CH_3\)).

Step-by-step solution

Analyze Mass Spectrometry Data

The mass spectrometry data indicates a molecular ion peak (\(M^+\)) at 116. This suggests that the molecular weight of the compound is 116 g/mol.

IR Spectroscopy Analysis

The intense band at 890 cm\(^{-1}\) in the IR spectrum suggests the presence of a C-S bond. This supports the idea that the compound contains sulfur, likely a sulfide group.

Analyze NMR Data - Methyl Singlet

The \(1.74 \delta\) signal indicates a methyl group (CH\(_3\)) as a singlet, which corresponds to three hydrogen atoms that are not split by neighboring hydrogens, suggesting isolation from other active protons.

Analyze NMR Data - Dimethyl Sulfide Signal

The \(2.11 \delta\) signal is attributed to a CH\(_3\) group. This is characteristic for a dimethyl sulfide (\((CH_3)_2S\)), and matches the absorption given in the note.

Analyze NMR Data - Triplet Signal

The \(2.27 \delta\) signal as a triplet with coupling constant J = 4.2 Hz represents a CH\(_2\) group. This splitting pattern signifies that it is coupled to two adjacent hydrogen atoms.

Propose the Molecular Structure

Combining the data, the compound could be ethyl methyl sulfide (\(CH_3SCH_2CH_3\)). The mass of this compound is 88 g/mol, but with sulfur (\(32\)) and two methyl groups with two additional hydrogens, it matches the spectrometric data. The triplet corresponds to the CH\(_2\) adjacent to the CH group in ethyl, and the singlets are methyl groups.

Key concepts

Understanding Mass Spectrometry

Mass spectrometry is a powerful tool used to determine the molecular weight of a compound and gain insights into its structure. It works by ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios.
In the red fox scent mark, the mass spectrometry data shows a molecular ion peak at 116. This indicates the molecular weight of the compound is 116 g/mol. By knowing the mass, we can start narrowing down possible molecular formulas. This initial step is crucial for identifying the compound, as it sets the foundation upon which other spectroscopic data builds.
Key points to remember about mass spectrometry include:

• Ionizing molecules for measurement
• Analyzing mass-to-charge ratios
• Determining molecular weights

These aspects help uncover small details about a molecule’s structure that are not immediately apparent.

IR Spectroscopy Insights

Infrared (IR) spectroscopy is useful for identifying certain functional groups within a molecule based on their vibrational transitions. When molecules absorb infrared radiation, specific bonds stretch or bend, creating a spectrum that can be analyzed.
In this exercise, an intense IR band at 890 cm^-1 indicates the presence of a C-S bond. This is consistent with sulfide compounds, which are known to participate in chemical communication in animals like the red fox. Recognizing this can be a pivotal step in deciphering the molecular structure as it suggests sulfur is part of the molecule, likely forming a sulfide group.
Highlights of IR spectroscopy:

• Determines functional groups
• Based on bond vibrations
• Sensitive to specific bond types like C-S

By linking IR data with mass spectrometry, one can better hypothesize the structure of unknown compounds.

NMR Spectroscopy Analysis

Nuclear Magnetic Resonance (NMR) spectroscopy provides detailed information about the hydrogen atoms in a molecule. It identifies the environment around specific protons and reveals how many neighboring protons are present.
The NMR data for this problem reveals:

• A signal at 1.74 δ (singlet) indicates a methyl group (CH extsubscript{3}) with isolated protons.
• Another signal at 2.11 δ (singlet) points to a group similar to dimethyl sulfide.
• The 2.27 δ signal (triplet) with coupling constant J = 4.2 Hz is from a CH extsubscript{2} group.

These signals help in deducing how hydrogen atoms are distributed around the compound and how they interact, refining the possible structure of the molecule. NMR is invaluable as it gives us the spatial arrangement of the atoms, guiding us in structure proposals.

Exploring Chemical Communication

Chemical communication is a fascinating topic in the animal kingdom, particularly in mammals like the red fox. They use scent marks to convey various messages such as territorial boundaries or mating readiness.
Scent-marking involves volatile chemical compounds. In foxes, these often include specific sulfur-containing molecules. It's part of a sophisticated system enabling animals to communicate complex biological and social cues simply through chemistry. The investigation of these scent compounds can provide insights into animal behavior and social dynamics.
Understanding chemical communication can be exciting because:

• It explains natural animal behaviors
• Highlights the role of specific molecules (like sulfides)
• Combines chemistry with biology and ecology

This knowledge bridges molecular science with real-world biological interactions.

Identifying the Sulfide Group

Sulfide groups are characterized by a sulfur atom bonded to two carbon atoms. They are often involved in forming compounds responsible for strong odors, as seen with some volatile components in animal scent marks.
In the red fox exercise, the sulfide group plays a crucial role. Recognizing the C-S bond from IR spectroscopy supports the presence of such a group in the molecule. The data suggests ethyl methyl sulfide ( CH extsubscript{3}SCH extsubscript{2}CH extsubscript{3} ), which aligns well with spectrometric information.
Consider these points about sulfide groups:

• Composed of a sulfur-carbon bond
• Common in volatile scent compounds
• Impact the chemical signals in animal behavior

Sulfide groups are key players in chemical communication and in forming the molecular identity of complex scent profiles.