Chapter 13

Question 1

What is the molecular ion?

M+1 and M+2 peaks?

Answer 1

The mass of the molecular ion is equal to molecular mass of the compound.
The molecular ion has the highest mass in spectrum, besides from isotopes. It is also the radical cation.
M+1 and M+2 account for isotopes.

Question 2

What is the Nitrogen rule?

Answer 2

A compound with an odd number of N atoms will have an odd molecular ion and a compound with an even number of N atoms will have an even molecular ion.

Question 3

What is the base peak?

Answer 3

The tallest peak in a mass spectrum

Question 4

Mass spectrum of monochloride

Answer 4

Shows two peaks for the molecular ion in a 3:1 ratio. (One at molecular ion peak and other at M+1 peak)

Question 5

Mass spectrum of monobromide

Answer 5

Shows two peaks for the molecular ion in a 1:1 ratio. (One at molecular ion peak and other at M+1 peak)

Question 6

What are the lower molecular weights shown in a mass spectrometer?

Answer 6

They are fragmentation a of radical cations that have lower molecular weights. Usually functional groups

Question 7

Difference between high and low resolution mass spectrometry

Answer 7

High resolution gives the molecular mass exactly( decimals), can tell us molecular formula.

Low resolution gives molecular mass in whole numbers.

Question 8

Relationship between wavelength and frequency

Answer 8

Wavelength and frequency are inversely related. As one increases other decreases.
λ=c/ν

Question 9

Relationship between energy and frequency

Answer 9

Energy of a photon is proportional to its frequency. The higher the frequency the higher the energy.
E=hν

Question 10

What is infrared spectroscopy?

Answer 10

Records frequencies of compounds that identify functional groups and different types of bonds

Question 11

IR absorption are reported in?

Answer 11

Wavenumbers 1/λ

Wavenumber a are proportional to higher frequencies and energies

Question 12

C-H, O-H, N-H bonds absorb at low or high frequency?

Answer 12

High frequency. (>2500)

Question 13

As bond strength increases the wavenumber increases or decreases?

Answer 13

Increases. Triple bonds absorb at higher wavenumber than double bonds.

Question 14

The higher the percent s-character the lower of higher the wavenumber?

Answer 14

Higher. Bond strength increases with higher s-character.

Question 15

What is mass spectrometry?

Answer 15

Measures the molecular weight of a compound. Also plots the molecular cations and fragments vs their mass

Question 16

For absorption to occur in an IR spectroscopy the energy of a photon must what?

Answer 16

The photon must match the difference between the two energy states in a molecule

Question 17

Absorption of IR light detects what changes in a molecule?

Answer 17

Vibrational motions of a molecule, including bending and stretching. Different kinds of bonds vibrate at different frequencies.

Question 18

Absorption frequencies in IR spectroscopy depend on which two factors?

Answer 18

Bond strength. Stronger the bond, higher the frequency.(Triple bonds strongest)
Atom mass. Lights atoms vibrate at higher frequencies. (Bonds to hydrogens always on left side of spectrum because light atom)

Question 19

For a bond to absorb in IR there must be a change in what?

Answer 19

There must be a dipole moment (polar). If molecule is nonpolar there won’t be an absorption.(IR inactive)