Mass Spectroscopy
The rule of 13 :-
In some step the rule of 13 is completed
Step 1:-
If m/z ( mass/ions) value is given then divided the given value for 13 and find the quotient value and reminder value.
Step 2:-
Quotient value show the number of carbon atoms present in the compound. The addition of reminder value and the quotient value show the number of hydrogen atoms present in the compound.
Step 3:-
If a Oxigen is present in the compound then,
number of carbon atoms = quotient value - 1
Number of hydrogen atoms = quotient value + Reminder value - 4
Step 4:-
If two oxigen atoms present in compound then,
Number of carbon atoms = quotient value - 2
Number of hydrogen atoms = quotient value + Reminder value - 8
Step 5:-
If one Nitrogen atoms present in the compound then,
Number of carbon atoms = quotient value - 1
Number of hydrogen atoms = quotient value + Reminder value - 2
Step 6:-
If two nitrogen atoms present in the compound then,
Number of carbon atoms = quotient value - 2
Number of hydrogen atoms = quotient value + Reminder value - 4
You notice the step number of carbon atoms decrease according to the number of Oxygen and nitrogen atoms present in the compound and number of hydrogen atoms decrease according to the multiplication of 4 and 2 .
Example 1:-
Draw the possibile structure for the ester that has a molecular ion with an m/z value of 74.
Solution:-
Dividing 74 by 13 then quotient value is 5 and Reminder value is 9.
We know that ester have two oxigen atoms.
Then,
Number of carbon atoms = 5-2 = 3
Number of hydrogen atoms = 5+9-8 = 6
So given compound molecular formula is C3H6O2.
Possibile structure:-
