0 votes
65 views
in Analytical Chemistry by (590 points)
A chemistry student needs to identify an unknown compound found at a crime scene using mass spectrometry. The compound has a molecular weight of 286 g/mol and the mass spectrum shows a strong peak at m/z = 180 and a weaker peak at m/z = 148. What is the possible molecular formula of the unknown compound?

1 Answer

0 votes
by (530 points)
To determine the possible molecular formula of the unknown compound, we can use the information provided by the mass spectrometry data. The molecular weight of the compound is 286 g/mol, and there are two significant peaks at m/z = 180 and m/z = 148.The strong peak at m/z = 180 likely represents the molecular ion  M+  or a significant fragment of the compound. The weaker peak at m/z = 148 could represent a fragment that is formed by the loss of a small neutral molecule from the molecular ion.Let's consider the difference between the molecular weight and the strong peak at m/z = 180:286 - 180 = 106This suggests that the compound may have lost a neutral molecule with a mass of 106 g/mol during fragmentation. Similarly, we can consider the difference between the strong peak and the weaker peak:180 - 148 = 32This suggests that the weaker peak may have formed by the loss of a neutral molecule with a mass of 32 g/mol from the strong peak.Now, we can try to identify the possible molecular formula of the unknown compound. Since the molecular weight is 286 g/mol, we can start by considering the most common elements found in organic compounds: carbon  C , hydrogen  H , oxygen  O , and nitrogen  N .A possible molecular formula for the compound could be CHON, which has a molecular weight of 286 g/mol. This formula contains 16 carbon atoms  12.01 g/mol each , 16 hydrogen atoms  1.01 g/mol each , 3 oxygen atoms  16.00 g/mol each , and 2 nitrogen atoms  14.01 g/mol each : 16  12.01  +  16  1.01  +  3  16.00  +  2  14.01  = 286 g/molThis molecular formula is consistent with the mass spectrometry data, as the compound could lose a neutral molecule with a mass of 106 g/mol  e.g., CHO  to form the strong peak at m/z = 180, and then lose another neutral molecule with a mass of 32 g/mol  e.g., O  to form the weaker peak at m/z = 148.However, it is important to note that mass spectrometry data alone may not be sufficient to definitively identify the molecular formula of an unknown compound. Additional analytical techniques, such as infrared spectroscopy, nuclear magnetic resonance spectroscopy, or elemental analysis, may be necessary to confirm the molecular formula and structure of the compound.

Related questions

Welcome to Sarvan Science Q&A, where you can ask questions and receive answers from other members of the community.
...