Question

What rule would you expect for the \(m / z\) values of fragment ions resulting from the cleavage of one bond in a compound with an odd number of nitrogen atoms?

Short answer

Answer: If a compound with an odd number of nitrogen atoms undergoes the cleavage of a bond, the m/z values of the fragment ions produced will either both be odd or both be even.

Step-by-step solution

Understanding the Nitrogen Rule

The Nitrogen Rule states that compounds with an odd number of nitrogen atoms have an odd nominal mass, while compounds with an even number of nitrogen atoms have an even nominal mass. This rule is important for determining the m/z values of fragment ions resulting from the cleavage of one bond.

Analyzing Fragment Ions Formation

When a compound with an odd number of nitrogen atoms undergoes the cleavage of one bond, it will generate fragment ions. Depending on the exact cleavage location, the fragment ions may or may not contain nitrogen atoms.

Consider Different Scenarios for Bond Cleavage

Let's consider the two possible scenarios following the cleavage: (a) The bond cleavage results in a fragment containing nitrogen: When this occurs, the fragment ion will have an odd number of nitrogen atoms resulting in an odd m/z value due to the Nitrogen Rule. In this case, the other fragment produced from cleavage will have an even m/z value since it has an even number of nitrogen atoms. (b) The bond cleavage results in a fragment without nitrogen: When this occurs, the fragment ion will have an even number of nitrogen atoms resulting in an even m/z value due to the Nitrogen Rule. In this case, the other fragment produced from cleavage will have an odd m/z value since it still contains an odd number of nitrogen atoms.

Formulate the Rule for m/z Values

Based on the scenarios discussed in step 3, it can be concluded that when a compound with an odd number of nitrogen atoms undergoes the cleavage of one bond, it produces fragment ions with either both odd m/z values or both even m/z values. Hence, the rule for m/z values of fragment ions resulting from the cleavage of one bond in a compound with an odd number of nitrogen atoms is: If a compound with an odd number of nitrogen atoms undergoes the cleavage of a bond, the m/z values of the fragment ions produced will either both be odd or both be even.