Mass Spect: Isotopes

Problem: Propose the number of carbons for a compound that exhibits the following peak in its mass spectrum: 

(M)+• at m/z = 72, relative height = 38.3% of base peak

(M+1)+• at m/z = 73, relative height = 1.7% of base peak 

5m

Problem: Predict the approximate height of the (M + 1) peak for the molecule icosane, molecular formula C20H42.

2m

Concept: Practice 3: Draw expected isotope pattern Intro

3m

Concept: Practice 3: Draw expected isotope pattern Solution

7m

Mass Spect: Isotopes Additional Practice Problems

Indicate which spectral technique, NMR, UV, or MS, would most readily allow differentiation between compounds.

a. NMR

b. UV

c. MS

Watch Solution

It is possible to identify that a given compound contains either chlorine or bromine from the presence of M and (M+2) peaks in the mass spectrum of the compound. State what species causes the (M+2) peaks in each of the following compounds.

 

(i) C3H7Cl

 

(ii) C2H5Br

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For which of the following compounds will the (M+2) + peak intensity be around one third the intensity of the molecular ion peak?

a CH3CH2CH2Br 
b CH3CH2CH2OH 
c CH3CH2CH2Cl 
d CH3CH2CH2NH2 
e none of these

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The formula of a compound with an even massed molecular ion will

a) contain an even number of nitrogen atoms.

b) contain an even number of halogen atoms.

c) contain an odd number of nitrogen atoms.

d) produce even massed fragment ions from one bond cleavage processes.

e) none of the above.

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Which of the following exists as two naturally occuring isotopes separated in mass by two amu and therefore shows an (M+2)+ peak roughly 1/3 as intense as M + in the mass spectrum. 

a) Bromine

b) Chlorine

c) Nitrogen

d) All of the above

e) None of the above

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Which of the following compounds will have an odd m/z value for the molecular ion?

a) I

b) II

c) III

d) IV

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Compounds containing chlorine or bromine usually show a strong _____ peak.

a) M+2

b) molecular ion

c) base

d) M+1

e) all of these

Watch Solution

Which compound below is expected to show an odd molecular ion in the mass spectrum and two IR signals between 3300 and 3500 cm-1?

a) H2NCH2CH2CH2CH2CH2CH2NH2

b) Diethylamine

c) Ethylamine

d) All of the above

e) None of the above

Watch Solution