Select the compound that was used to generate the mass spectrum. 2-methylheptane heptane 2,4-dimethylpentane hexane
The concept used to solve this problem is mass spectroscopy. Mass spectrometry is a technique used for determining the chemical composition of an unknown substance.
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A mass spectrum is normally presented as a vertical bar graph, where each bar represents an ion having a specific mass-to-charge ratio
and the relative abundance of the ion is indicated by the length of the bar. The mass spectrum records the mass-to-charge ratios
and the intensities of the fragment and molecular ions.
From the given spectrum, it is found that the
1. Molecular ion peak is 100 and this indicates that the mass of the substance investigation is 100.
2. The base peak is 43.
In order to determine the formula, we use the 13-rule.
Here, m is mass of compound. Substitute m as 100 g.
Therefore, the formula has 7 carbon atoms. Now, for determining the remaining formula, multiply the remainder (r) with 13 as follows:
Substitute r as 0.69 in the above expression as follows:
Therefore, a molecule will have the following number of Hydrogen (H) atoms,
The formula is C7H16. This is the formula for alkanes.
Looking at the given spectra, various groups are assigned to the peaks:
Starting from the first peak at 15, it indicates the loss of a CH3 group.
1. 29-15=14, indicating the fragmentation of a CH2 group.
2. 43-29=14, indicating the fragmentation of a CH2 group.
3. 57-43=14, indicating the fragmentation of a CH2 group.
4. 71-57=14, indicating the fragmentation of a CH2 group.
5. 100-57=29 indicating the remaining C2H5 group.
Based on the above, fragmentation pattern, we identify various groups present. The possible structure for the compound is: