Topic 7 Modern Analytical Techniques

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Total cards: 24•Content version: v4•Public deck•Updated: 8/1/2026

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Front (Question)

Molecular ion peak

Back (Answer)

Indicates the species formed from the molecule by the loss of one electron.

Front (Question)

Fragmentation

Back (Answer)

Occurs when the molecular ion breaks into smaller pieces.

Front (Question)

Base peak

Back (Answer)

Indicates the peak with the greatest abundance. The tallest peak. Relative intensity of 100%. It represents the most stable fragment.

Front (Question)

In a mass spectrum of an element, what does a peak represent?

Back (Answer)

An isotope of an element.

Front (Question)

The peak furthest right on an m/z spectrum

Back (Answer)

• Has the greatest m/z value. • Is the molecular ion peak. • Indicates the relative molecular mass of the organic compound.

Front (Question)

Equation for the formation of a molecular ion peak (example: butane):

Back (Answer)

C4H10 + e- –> C4H10 + 2e-

Front (Question)

How does the molecular ion peak form?

Back (Answer)

An electron collides with the molecule, and knocks out an electron to form a positive ion.

Front (Question)

M + 1 peak

Back (Answer)

Small peak just right of the molecular ion peak due to the presence of the 13C isotope of carbon.

Front (Question)

13C

Back (Answer)

1% of all naturally-occurring carbon atoms.

#10

Front (Question)

14C

Back (Answer)

Used in radiocarbon dating. The proportion of 14C atoms in a sample of an organic compound is negligible.

#11

Front (Question)

What causes peaks with smaller m/z values?

Back (Answer)

Fragmentation, rearrangement reactions and the loss of more than one electron.

#12

Front (Question)

Rearrangement

Back (Answer)

Beyond the spec. Often unpredictable. Explains the high number of peaks in some spectra.

#13

Front (Question)

When a C-C bond breaks by fragmentation, what is produced?

Back (Answer)

• Another positive ion. • A neutral species, usually a radical.

#14

Front (Question)

y-axis on a mass spectrum

Back (Answer)

Relative intensity (%) 0%-100%

#15

Front (Question)

x-axis on a mass spectrum

Back (Answer)

m/z (no units) Usually 0 to just past the molecular ion peak.

#16

Front (Question)

What causes all the peaks formed by fragmentation?

Back (Answer)

Positive ions as radicals are not detected in a mass spectrometer.

#17

Front (Question)

The breaking of a carbon-hydrogen bond

Back (Answer)

Can occur, but is not considered fragmentation.

#18

Front (Question)

Fragmentation of the molecular ion of ethane (example)

Back (Answer)

(CH3–CH3)+dot –> CH3 dot + CH3+ Fragments to form a methyl cation + a methyl radical, as there is only one C-C bond. Both methyls are equally likely to form the cation, so the products are identical. Thus, the spectrum does not depend on how the bond breaks. There is a peak at m/z= 15.

#19

Front (Question)

Fragmentation of the molecular ion of propane (example)

Back (Answer)

There are two equivalent C-C bonds, so there are two possible peaks that form: the methyl m/z= 15 cation & the ethyl m/z= 29 cation.

#20

Front (Question)

What is the possible ion for an m/z value of 15?

Back (Answer)

CH3+

#21

Front (Question)

What is the possible ion for an m/z value of 17?

Back (Answer)

OH+

#22

Front (Question)

What is the possible ion for an m/z value of 28?

Back (Answer)

CO+

#23

Front (Question)

What are the possible ions for an m/z value of 29?

Back (Answer)

CH3CH2+ & CHO+

#24

Front (Question)

What is the possible ion for an m/z value of 31?

Back (Answer)

CH2OH+