Unit 15 – IR & MS

Spectroscopy is a technique used to determine the _________________________.

Most techniques are ____________________ (it destroys ____________ sample).

__________________ measures the amount of _______________ by the sample as

a function of __________________.

Types of Spectroscopy

Infrared (___) spectroscopy measures the ____________________________ in a

molecule and is used to determine the ______________________.

Mass spectrometry (___) _____________________ and measures their ______.

MS can give the _________________ of the compound and _______________.

Nuclear magnetic resonance (_____) spectroscopy analyzes the environment of

the ____________ in a compound. This gives useful clues as to the _______ and

other ____________________ present.

Ultraviolet (___) spectroscopy uses electronic transitions to determine

__________________________.

Electromagnetic Radiation

Electromagnetic radiation: __________and other forms of ________________

Wavelength (___ ): the distance between ____________________ on a wave

Frequency (___ ): the number of __________ of a wave that pass a given point in

_____________

Hertz (___): the unit in which _____________ is reported; ____ (read “per

second”)

Common units used to express wavelength

Angstrom (Å) 1 Å = 10-10 m

Relationto MeterUnit

1 mm = 10-3 m

1 nm = 10-9 m1 m = 10-6 m

Nanometer (nm)Micrometer (m)Millimeter (mm)Meter (m) ----

Molecular spectroscopy: the study of which frequencies of electromagnetic

radiation are ____________________ by a particular substance and the correlation

of these frequencies with details of ____________________

– we study ____ types of molecular spectroscopy

Vibrational energy levels

Nuclear spin states

Electronic energy levelsInfrared

Radio fequency

Ultraviolet-visible

Absorption ofElectromagneticRadiation Results in Transition Between

Region of theElectromagneticSpectrum

Nuclear magneticresonanceInfraredUltraviolet-visible

Type of Spectroscopy

The IR Region

From right below the _______________ to just above the highest

_____________________________________ frequencies .

More common units are _______________, or ______, the _________________

of the wavelength in centimeters.

Wavenumbers are proportional to ___________________________.

The vibrational IR extends from 2.5 x 10-6 m (_______) to 2.5 x 10-5 m (______)

– the frequency of IR radiation is commonly expressed in ______________

– wavenumber _____: the number of _____________, with units cm-1 (read

reciprocal centimeters)

– expressed in wavenumbers, the ______________________ extends from

__________________________________

Fingerprint Region of the Spectrum

No two molecules will give exactly the same IR spectrum (except _________).

Fingerprint region is between ________________, and has the most complex

vibrations.

The region between ______________ has the most common vibrations and we can

use it to get information about _______________________ in the molecule.

The Infrared Spectrometer

IR Spectrum of Alkanes

An alkane will show stretching and bending frequencies for ____ and ____ only.

The _____ stretching is a broad band between ____________, a band present in

virtually all organic compounds.

In this example, the importance lies in what is not seen, i.e., the ____________

indicates the presence of ________________________.

IR Spectrum of Alkenes

The most important absorptions in the 1-hexene are the _____ stretch at ________,

and the ____________ stretch at _____________.

Notice that the bands of the _______ are present in the ____________.

IR Spectrum of Alkynes

IR spectrum of 3-methyl-2-butanone

Molecular Vibrations

Atoms joined by _________ undergo continual vibrations ___________________

The energies associated with these vibrations are __________; within a molecule,

only ____________________________ are allowed

The ____________ associated with transitions between vibrational energy levels

correspond to ___________ in the infrared region, _________________

For a molecule to absorb IR radiation the bond undergoing vibration must be

_________ and its vibration must cause a ___________________ in the bond

____________________

Covalent bonds which do not meet these criteria are said to be ______________

The C-C _____________ bonds of ______________________ alkenes and

alkynes, for example, are IR inactive because they _____________________

For a nonlinear molecule containing ___atoms, there are _____ allowed

fundamental ______________

For even a relatively small molecule, a ____________ of vibrational energy levels

exist and patterns of IR absorption can be very _____________

The simplest vibrational motions are ____________________________

Fundamental stretching and bending vibrations for a methylene group

Consider two covalently bonded atoms as two vibrating masses connected by a

________

the total energy is _______________ to the frequency of vibration

the frequency of a _____________ vibration is given by an equation derived

from _________________________

K = a ____________, which is a measure of the bonds’ _________; force

constants for single, double, and triple bonds are approximately 5, 10, and 15 x 105

dynes/cm

m = __________ of the two atoms, __________________, where m is the mass of

the atoms in grams

From this equation, we see that the _________ of a stretching vibration

is ____________ to the ____________ of the vibrating bond

is ____________________ to the masses of the atoms connected by the bond

The intensity of absorption depends primarily on the polarity of the vibrating bond

Correlation Tables

Characteristic IR absorptions for the types of bonds and functional groups we deal

with most often

C-HN-HO-H

C=OC=C

C-O 1000-1250 strong

weak to medium1600-16801630-1820 strong

2700-3300 weak to medium

weak to strong3200-3650medium3100-3550

IntensityStretchingFrequency (cm-1)Bond

Hydrocarbons

C-H

CH3

C=CC-H

C-HC C

C-C

C-HC=CC-H

Intensity

2850 - 3000 Medium

Stretching 3300 Medium to strongStretching 2100-2250 Weak

Weak to medium1600 - 1680StretchingWeak to medium3000 - 3100Stretching

Alkyne

Alkene

AlkaneVibration

Stretching

Hydro-carbon

Frequency(cm-1)

Bending 1450-1475 MediumBending 1375 and 1450 Weak to medium(Not useful for interpretation - too many bands

AreneStretching 3030 Weak to medium

Medium1450-1600StretchingBending 690-900 Strong

Alkanes: IR spectrum of decane

Alkenes: IR spectrum of cyclohexene

Alkynes: IR spectrum of 1-octyne

Aromatics: IR spectrum of toluene

Alcohols

O-H (free)O-H (H bonded)C-O

Bond IntensityFrequency, cm-1

Medium1000 - 1250Medium, broad3200 - 3500

3600-3650 Weak

IR spectrum of 1-hexanol

Ethers: IR spectrum of dibutyl ether

IR spectrum of anisole

Amines: IR spectrum of 1-butanamine

IR of Molecules with C=O Groups

C=O

C=O

C-H

O HRCOHO

RCHO

RCR'O

C=O

Strong1700-1725StretchingCarboxylic acids

Aldehydes

VibrationCarbonyl Group Frequency(cm-1) Intensity

Stretching 1630-1820 StrongStretching 2720 Weak

Stretching 2500-3300 Strong (broad)

KetonesStretching 1630-1820 Strong

C=O

sp3 C Osp2 C O

C=O

C=ON H

CNRC N

RCOCRO O

RCOR'O

RCNH2O

C O Stretching 900-1300 Strong

Strong1735-1800StretchingCarboxylic esters

Stretching 1000-1100 StrongStretching 1200-1250 Strong

Acid anhydridesStretching 1740-1760 and

1800-1850Strong

Strong1630-1680StretchingAmides

Stretching 3200, 3400 Medium(1° amides have two N-H stretches)(2° amides have one N-H stretch)

NitrilesStretching 2200-2250 Medium

Aldehydes and Ketones: IR spectrum of menthone

Carbonyl groups

The position of _____ stretching vibration is sensitive to its molecular environment

as ring size decreases and angle strain increases, absorption shifts to a higher

frequency

conjugation shifts the C=O absorption to lower frequency

Carboxylic acids: IR spectrum of pentanoic acid

Esters: IR of ethyl butanoate

Summary of IR Absorptions

Strengths and Limitations

IR alone cannot determine a structure.

Some signals may be _____________.

The functional group is _________________.

The _________of a signal is definite proof that the functional group is _______.

Correspondence with a known sample’s IR spectrum _____________________

of the compound.

Mass Spectrometry

Molecular weight can be obtained from a __________________.

A beam of ______________________________ breaks the molecule apart.

_________________ technique, the sample ___________________________.

The masses of the ____________ and their _____________________ reveal

information about the structure of the molecule.

Mass Spectrometer

Separation of Ions

A beam of electrons causes molecules to _____________________________.

The mixture of ions is _________________ and passes through a

__________________, where the paths of lighter ions are bent more than those

of _____________ atoms.

By varying the magnetic field, the spectrometer plots the __________________

of each mass.

The exact radius of curvature of an ion's path depends on its

____________________, symbolized by _____. In this expression, ___is the

mass of the ion (in amu) and ___is its charge.

The vast majority of ions have a ____ charge, so we consider their path to be

curved by an amount that depends __________________________.

The Mass Spectrum

In the spectrum, the ___________ is called the __________ and it is assigned an

abundance of _______. The % abundance of all other peaks are given

____________________________________.

The molecular ion (_____) corresponds to the mass of the ________________.

Gas Chromatography–Mass Spectrometry (GC–MS)

The gas chromatograph column separates the mixture into its ________________.

The mass spectrometer scans ____________ of the components as they

_________________________.