Question

Halogenated compounds are particularly easy to identify by their mass spectra because chlorine and bromine occur naturally as mixtures of two abundant isotopes. Chlorine occurs as 35Cl (75.8%) and 37Cl (24.2%); bromine occurs as 79Br (50.7%) and 81Br (49.3%). For the compound Chlorocyclohexane, C6H11Cl: At what masses do the molecular ions occur? (List in order of increasing mass separated by commas, e.g. 120,122.) What are the percentages of each molecular ion?

Answer 1

Answer:

The increasing order of masses of molecule ions:

118 g/mol(75.8%) ,  120 g/mol(24.2%)

Explanation:

Chlorine occurs as 35-Cl (75.8%) and 37-Cl (24.2%).

Atomic mass of 35-Cl = 35 g/mol

Atomic mass of 37-Cl = 37 g/mol

Mass of Chlorocyclohexane in which 35-cl is present as a chlorine atom: $C_6H_{11}Cl$

$=6\times 12 g/mol+11\times 1 g/mol+1\times 35 g/mol=118 g/mol$

Mass of Chlorocyclohexane in which 37-Cl is present as a chlorine atom: $C_6H_{11}Cl$

$=6\times 12 g/mol+11\times 1 g/mol+1\times 37 g/mol=120 g/mol$

The increasing order of masses of molecule ions:

118 g/mol(75.8%) < 120 g/mol(24.2%)