Use the data below from an electron impact mass spectrum of a pure compound to deduce its structure.
Mass Spectrum
M/z Relative intensity
66 32
64 100
49 26
29 72
28 83
27 60
The 3:1 doublet at m/z=64 and 66 is the characteristic "isotope cluster" for one chlorine atom. The compound contains chlorine.
The molecular ion (and molecular weight) is 64. (M/z=66 is the 37Cl isotope peak at M+2.)
Subtracting the mass of 35Cl from the mass of the molecular ion, 64, leaves 29 daltons unaccounted for. This is exactly the mass of ethyl. Thus, this is probably chloroethane.
The peak at m/z=29 is ethyl cation.
That at m/z=28 is ethene radical cation(CH2=CH2 .+) from loss of HCl from the molecular ion.
These and the peak at m/z=49 from loss of methyl from the molecular ion support this conclusion.
To deduce the structure of the pure compound based on the given electron impact mass spectrum, we need to consider the mass (M/z) values and their relative intensities.
1. The most intense peak in the spectrum appears at m/z 64 with a relative intensity of 100. This indicates that the compound has a molecular ion peak at this mass. This means the compound has a molecular weight of 64.
2. Another significant peak in the spectrum is observed at m/z 28 with a relative intensity of 83, which suggests the presence of a fragment with this mass. This fragment likely contains a carbon atom since its mass is even.
3. There is also a peak at m/z 29 with a relative intensity of 72, indicating the presence of a fragment with a mass of 29. This fragment could correspond to a methyl group (CH3) or a nitrogen atom (N).
4. The peak at m/z 49 with a relative intensity of 26 may correspond to a fragment containing a nitrogen atom (N).
5. The peaks at m/z 27 with a relative intensity of 60 and at m/z 66 with a relative intensity of 32 can be linked to the fragments observed earlier.
Based on these observations, one possible structure for the compound can be deduced as follows:
- The molecular ion peak at m/z 64 suggests a molecular formula of C4H8 (since the compound's molecular weight is 64 and we know it contains only carbon and hydrogen).
- The presence of the fragment at m/z 28 suggests the presence of a methyl group (CH3) in the compound.
- The peak at m/z 29 suggests the presence of a methyl group (CH3) or a nitrogen atom (N).
- The presence of a nitrogen atom is further supported by the peak at m/z 49.
Based on these deductions, one possible structure for the compound could be:
CH3CH2CH2CH3
This structure represents a butane (C4H10) molecule, which matches the given mass spectrum data. However, please note that this is just one possible structure and other isomers with the same molecular weight could exist. Further analysis and information might be needed to confirm the exact structure.
To deduce the structure of a compound using the data from an electron impact mass spectrum, we need to analyze the M/z values (mass-to-charge ratio) and the relative intensities of the peaks.
Here's how you can approach it:
1. Identify the base peak: The base peak is the peak with the highest relative intensity. In this case, the M/z 64 peak has a relative intensity of 100, so it is the base peak.
2. Look for fragment peaks: Fragment peaks are created when the compound undergoes fragmentation during the electron impact. Fragments are formed by breaking bonds within the molecule. Start by looking for peaks that are lower than the base peak but higher than the noise level. Peaks that are one or two units higher in M/z than the base peak are often due to the loss of a methyl (CH3) or methylene (CH2) group.
In this case, we can observe peaks with M/z values of 66 and 49. The M/z 66 peak can be explained by the presence of a methyl group (CH3+) as it is only two mass units higher than the base peak (64). The M/z 49 peak indicates the loss of a methyl group (CH3) from the original molecule.
3. Analyze the remaining peaks: After identifying the fragment peaks, we can focus on the remaining peaks for clues about the compound's functional groups. In this case, we have M/z peaks of 29, 28, and 27.
The M/z 29 peak indicates a molecular ion peak (M+) which suggests the presence of a fragment with a mass of 29. This mass corresponds to the methyl cation (CH3+). Therefore, the presence of a methyl group can be confirmed.
The M/z 28 peak has a relatively high intensity and may correspond to the loss of one hydrogen atom (H) from the original molecule. This suggests the presence of a hydrogen atom attached to another fragment.
The M/z 27 peak can be explained by the loss of a hydrogen atom (H) from the M/z 28 fragment. This suggests the presence of a hydrogen attached to another fragment, which further suggests the presence of a functional group containing a hydrogen atom.
Based on the identified peaks and their relative intensities, we can deduce the possible structure:
- Methyl group (CH3)
- Fragment with molecular weight 28, possibly containing a hydrogen atom
- Fragment with molecular weight 27, possibly containing a functional group with a hydrogen atom attached
Taking into account all the available information, a possible structure for the compound could be:
CH3 - (Fragment with M/z 28) - (Functional group with M/z 27)