UV / VISIBLE SPECTROSCOPY

Spectroscopy
 It is the branch of science that deals with the study of
interaction of matter with light.
OR
 It is the branch of science that deals with the study of
interaction of electromagnetic radiation with matter.
Electromagnetic
Radiation
 Electromagnetic Radiation
 Electromagnetic radiation consist of discrete
packets of energy which are called as
photons.

 A photon consists of an oscillating electric

field (E) & an oscillating magnetic field (M)
which are perpendicular to each other.
Electromagnetic Radiation
 Frequency (ν):
 It is defined as the number of times electrical
field radiation oscillates in one second.
 The unit for frequency is Hertz (Hz).
1 Hz = 1 cycle per second

 Wavelength (λ):
 It is the distance between two nearest parts of
the wave in the same phase i.e. distance
between two nearest crest or troughs.
Electromagnetic Radiation

 The relationship between wavelength &

frequency can be written as:
c=νλ
 As photon is subjected to energy, so
E = hν = hc/ λ
Electromagnetic Radiation
Electromagnetic Radiation

Violet 400 - 420 Yellow 570 - 585

nm nm
Indigo 420 - 440 Orange 585 - 620
nm nm
Blue 440 - 490 Red 620 - 780
nm nm
Green 490 - 570
nm
Principles of
Spectroscopy
Principles of Spectroscopy
 The principle is based on the measurement
of spectrum of a sample containing atoms /
molecules.

 Spectrum is a graph of intensity of absorbed

or emitted radiation by sample verses
frequency (ν) or wavelength (λ).

 Spectrometer is an instrument design to

measure the spectrum of a compound.
Principles of Spectroscopy
1. Absorption Spectroscopy:
 An analytical technique which concerns with
the measurement of absorption of
electromagnetic radiation.

 e.g. UV (185 - 400 nm) / Visible (400 - 800

nm) Spectroscopy, IR Spectroscopy (0.76 - 15
μm)
Principles of Spectroscopy
2. Emission Spectroscopy:
 An analytical technique in which emission
(of a particle or radiation) is dispersed
according to some property of the
emission & the amount of dispersion is
measured.

 e.g. Mass Spectroscopy

Interaction of EMR
with
Matter
 Interaction of EMR with matter
1.Electronic Energy Levels:
 At room temperature the molecules are in the lowest energy
levels E0.

 When the molecules absorb UV-visible light from EMR, one

of the outermost bond / lone pair electron is promoted to
higher energy state such as E1, E2, …En, etc is called as
electronic transition and the difference is as:
∆E = h ν = En - E0 where (n = 1, 2, 3, … etc)
∆E = 35 to 71 kcal/mole
 Interaction of EMR with matter
2.Vibrational Energy Levels:
 These are less energy level than electronic energy levels.
 The spacing between energy levels are relatively small i.e.
0.01 to 10 kcal/mole.
e.g. when IR radiation is absorbed, molecules are excited from
one vibrational level to another or it vibrates with higher
amplitude.
3. Rotational Energy Levels:
 These energy levels are quantized & discrete.

 The spacing between energy levels are even smaller than

vibrational energy levels.
∆Erotational < ∆Evibrational < ∆Eelectronic
Beer-Lambert’s
Law
Beer Lamberts Law:
A=εbc
A=absorbance
ε =molar absorbtivity with units of L /mol.cm
b=path length of the sample (cuvette)
c =Concentration of the compound in solution,
expressed in mol /L
Electronic
Transitions
The possible electronic transitions are
1 • σ → σ* transition
2 • π → π* transition

3 • n → σ* transition

4 • n → π* transition

5 • σ → π* transition

6 • π → σ* transition
 1 • σ → σ* transition

• σ electron from orbital is excited to

corresponding anti-bonding orbital σ*.

• The energy required is large for this

transition.

• e.g. Methane (CH4) has C-H bond only and

can undergo σ → σ* transition and shows
absorbance maxima at 125 nm.
 2 • π → π* transition

• π electron in a bonding orbital is excited to

corresponding anti-bonding orbital π*.

• Compounds containing multiple bonds

like alkenes, alkynes, carbonyl, nitriles,
aromatic compounds, etc undergo π → π*
transitions.
e.g. Alkenes generally absorb in the
region 170 to 205 nm.
 3 • n → σ* transition

• Saturated compounds containing atoms

with lone pair of electrons like O, N, S and
halogens are capable of n → σ* transition.

• These transitions usually requires less

energy than σ → σ* transitions.

• The number of organic functional groups

with n → σ* peaks in UV region is small
(150 – 250 nm).
 4 • n → π* transition

• An electron from non-bonding orbital is

promoted to anti-bonding π* orbital.

• Compounds containing double bond

involving hetero atoms (C=O, C≡N, N=O)
undergo such transitions.

• n → π* transitions require minimum

energy and show absorption at longer
wavelength around 300 nm.
 5 • σ → π* transition
& • π → σ* transition 6
• These electronic transitions are forbidden
transitions & are only theoretically possible.

• Thus, n → π* & π → π* electronic

transitions show absorption in region above
200 nm which is accessible to UV-visible
spectrophotometer.

• The UV spectrum is of only a few broad of

absorption.
The possible electronic transitions can
graphically shown as:
Terms used
in
UV / Visible
Spectroscopy
Chromophore
The part of a molecule responsible for imparting color,
are called as chromospheres.
OR
The functional groups containing multiple bonds
capable of absorbing radiations above 200 nm due to n
→ π* & π → π* transitions.

e.g. NO2, N=O, C=O, C=N, C≡N, C=C, C=S, etc

Auxochrome
The functional groups attached to a chromophore which
modifies the ability of the chromophore to absorb light ,
altering the wavelength or intensity of absorption.
OR
The functional group with non-bonding electrons that
does not absorb radiation in near UV region but when
attached to a chromophore alters the wavelength &
intensity of absorption.
Auxochrome
e.g. Benzene λmax = 255 nm

OH
Phenol λmax = 270 nm

Aniline λmax = 280 nm NH2

Absorption
& Intensity
Shifts
 1 • Bathochromic Shift (Red Shift)
• When absorption maxima (λmax) of a
compound shifts to longer wavelength, it is
known as bathochromic shift or red shift.

• The effect is due to presence of an

auxochrome or by the change of solvent.

• e.g. An auxochrome group like –OH, -OCH3

causes absorption of compound at longer
wavelength.
 1 • Bathochromic Shift (Red Shift)
• In alkaline medium, p-nitrophenol shows
red shift. Because negatively charged oxygen
delocalizes more effectively than the
unshared pair of electron.
- -
O + O O + O
N N

-
OH

Alkaline
medium -
OH O

p-nitrophenol
λmax = 255 nm λmax = 265 nm
 2 • Hypsochromic Shift (Blue Shift)
• When absorption maxima (λmax) of a
compound shifts to shorter wavelength, it is
known as hypsochromic shift or blue shift.

• The effect is due to presence of an group

causes removal of conjugation or by the
change of solvent.
 2 • Hypsochromic Shift (Blue Shift)
• Aniline shows blue shift in acidic medium, it
loses conjugation.

+ -
NH2 + NH 3 Cl
H
Acidic
medium

Aniline
λmax = 280 nm λmax = 265 nm
 3 • Hyperchromic Effect
• When absorption intensity (ε) of a
compound is increased, it is known as
hyperchromic shift.
• If auxochrome introduces to the compound,
the intensity of absorption increases.

N N CH3

Pyridine 2methylpyridine
λmax = 257 nm λmax = 260 nm
ε = 2750 ε = 3560
 4 • Hypochromic Effect

• When absorption intensity (ε) of a

compound is decreased, it is known as
hypochromic shift.

CH3

Naphthalene 2-methyl
naphthalene
ε = 19000 ε = 10250
Shifts and Effects
Hyperchromic shift

Blue Red
Absorbance ( A )

shift shift

Hypochromic shift

λmax
Wavelength ( λ )
Beer-Lambert’s Law
Statement: for a given material sample path length and concentration of the
sample are directly proportional to the absorbance of the light.
Beer-Lambert Law derivation helps us to define the relationship of the
intensity of visible UV radiation with the exact quantity of substance present.
Used in modern-day labs for testing of medicines, organic chemistry and to
test with quantification.
The Beer-Lambert law is expressed as:
A = εbc
where,
• A is the amount of light absorbed for a particular wavelength by the sample
• ε is the molar extinction coefficient
• b is the distance covered by the light through the solution
• c is the concentration of the absorbing species
Following is an equation to solve for molar extinction coefficient:
ϵ=A/bc
 DERIVATION OF BEERS-LAMBERTS LAW
Experimental measurements are usually made in terms of transmittance (T), which is defined as:
T = I / Io
where I is the light intensity after it passes through the sample and Io is the initial light intensity.
The relation between A and T is:
A = -log T = - log (I / Io).
Absorption of light by a sample

NOTE: Modern absorption instruments can usually display the data as either
transmittance, %-transmittance, or absorbance. An unknown concentration of an
analyte can be determined by measuring the amount of light that a sample absorbs
and applying Beer's law. If the absorptivity coefficient is not known, the unknown
concentration can be determined using a working curve of absorbance versus
concentration derived from standards.
The Beer-Lambert law can be derived from an approximation for the absorption coefficient
for a molecule by approximating the molecule by an opaque disk whose cross-sectional
area, σ, represents the effective area seen by a photon of frequency w. If the frequency of
the light is far from resonance, the area is approximately 0, and if w is close to resonance
the area is a maximum. Taking an infinitesimal slab, dz, of sample:

Io is the intensity entering the sample at z=0, Iz is the intensity entering the infinitesimal slab
at z, dI is the intensity absorbed in the slab, and I is the intensity of light leaving the sample.
Then, the total opaque area on the slab due to the absorbers is σ * N * A * dz. Then, the
fraction of photons absorbed will be σ * N * A * dz / A so,
dI/ Iz = - σ * N * dz
Derivation continued…..
Integrating this equation from z=0 to z=b gives,
ln(I)-ln(Io) = - σ * N * b
OR -ln (I-Io) = σ * N * b
Since N(molecules/cm3) * (1 mole / 6.023x1023 molecules) * 1000 cm3 / liter
= c (moles/liter) and 2.303 * log(x) = ln(x) then,
-log (I-Io) = σ *(6.023x1020 / 2.303)* c * b
-log (I-Io) = A= ε * b * c
Where ε = σ *(6.023x1020 / 2.303) = σ* 2.61x1020
OR For each wavelength of light passing through the spectrometer, the intensity of the light passing through
the reference cell is measured. This is usually referred to as Io that’s I for Intensity.

Figure : Light absorbed by sample in a cuvette

• The intensity of the light passing through the sample cell is also measured for that wavelength -
given the symbol, I. If I is less than Io, then the sample has absorbed some of the light
(neglecting reflection of light off the cuvette surface). A simple bit of math is then done in the
computer to convert this into something called the absorbance of the sample - given the
symbol, A.
• The absorbance of a transition depends on two external assumptions.
1.The absorbance is directly proportional to the concentration (c) of the solution of the sample
used in the experiment.
2.The absorbance is directly proportional to the length of the light path (l), which is equal to the
width of the cuvette.
Assumption one relates the absorbance to concentration and can be expressed as,
A∝c (1)
The absorbance (A) is defined via the incident intensity Io and transmitted intensity I by
A=log10(Io/I) (2)
Assumption two can be expressed as,
A∝l (3)
Combining equations 1 & 3,
A∝c l (4)
The proportionality can be converted in to equality by including a proportionality constant (ε),
A∝ε c l (5)
This formula is the common form of the Beer-Lambert Law, although it can be also written in terms of
intensities:
A=log10(Io/I) = ε c l (6)
The constant ϵ is called molar absorptivity or molar extinction coefficient and is a measure of the
probability of the electronic transition. On most of the diagrams you will come across, the absorbance
ranges from 0 to 1, but it can go higher than that. An absorbance of 0 at some wavelength means that no
light of that particular wavelength has been absorbed. The intensities of the sample and reference beam
are both the same, so the ratio Io/I is 1 and the log10 of 1 is zero.
What are the limitations of Beer-Lambert law?

• A diluted solution is used

• There shouldn’t be a scattering of
the light beam
• Monochromatic electromagnetic
radiation should be used
Why does Beer-Lambert law fails at higher
concentrations?
 Beer-Lambert law fails at higher concentrations
because the linearity of the law is limited to
chemical and instrumental factors.
 When the solution has higher concentrations, the
proximity between the molecules of the solution is
so close that there are deviations in the
absorptivity.
 When the concentration is high, the refractive
index changes.
Deviation from Beer’s law
• Real limitation to beer’s law
• Apparent chemical deviation.
• Apparent instrumental deviation from
Polychromatic Radiation.
• Apparent instrumental deviation from in
presence of stray radiation
State the situations when Beer’s law is not obeyed.
• When different types of molecules are in
equilibrium with each other.
• An association complex is formed by the
solute and the solvent.
• When fluorescent compounds are used.
• When thermal equilibrium is attained between
the excited state and the ground state.
Choice of Solvents
A solvent is a liquid that dissolves another solid, liquid, or gaseous
solute, resulting in a solution at specified temperature.
Solvents can be broadly classified into two categories:
1. Polar
2. 2.Non-Polar.
3. A drug may show varied spectrum at particular wavelength in one
particular condition but shall absorb partially at the same wavelength
in another conditions.
4. These appeared changes in the spectrum are exclusively due to
various characteristic features namely
A. Nature of solvent
B. Nature of absorption band
C. Nature of the solute
EFFECT OF SOLVENT:
The solvent exerts a profound influence on the quality
and shape of spectrum.
The absorption spectrum of pharmaceutical substance
depends practically upon the solvent that has been
employed to solubilize the substance.
A drug may absorb a maximum radiation energy at
particular wavelength in one solvent but shall absorb
partially at the same wavelength in another solvent.
Eg: acetone in n-hexane λ max at 279nm.
Acetone in water λ max at 264.5nm.
NATURE OF SOLVENT:
 Most commonly used solvent is 95% ethanol. It is best solvent as
1. It is cheap
2. Has good dissolving power
3. Does not absorbs radiations above 210nm.
 In choosing a solvent, consideration must be given not only to its
transparency, but also to its possible effects on absorbing system.
 There are other solvents which are transparent above 210nm.
 Benzene, chloroform , carbon tetrachloride cannot be used
because they absorb in the range of 240-280 nm.
CHOICE OF SOLVENT
A suitable solvent for UV-spectroscopy should
meet the following requirements.
1. It should not itself absorb radiations in the
region under investigation.
2. It should be less polar so that it has
minimum interaction with the solute
molecules.
CHOICE OF SOLVENT
Solvent λ of absorption
Water 191 nm
Ether 215 nm
Methanol 203 nm
Ethanol 204 nm
Chloroform 237 nm
Carbon tetrachloride 265 nm
Benzene 280 nm
Tetrahydrofuran 220 nm
PRINCIPLES OF UV
- VISIBLE
SPECTROSCOPY
Principle
 The UV radiation region extends from 10 nm to 400
nm and the visible radiation region extends from 400
nm to 800 nm.
Near UV Region: 200 nm to 400 nm
Far UV Region: below 200 nm
 Far UV spectroscopy is studied under vacuum
condition.
 The common solvent used for preparing sample to be
analyzed is either ethyl alcohol or hexane.
 Instrumentation
Components of UV-Visible spectrophotometer
 Source
 Filters & Monochromator
 Sample compartment
 Detector
 Recorder
 Five Basic Optical Instrument Components

 1) Source – A stable source of radiant energy at the desired

wavelength (or range).
 2) Wavelength Selector – A device that isolates a restricted
region of the EM spectrum used for measurement
(monochromators, prisms & filters).
 3) Sample Container – A transparent container used to
hold the sample (cells, cuvettes, etc).
 4) Detector/Photoelectric Transducer – Converts the
radiant energy into a useable signal (usually electrical).
 5) Signal Processor & Readout – Amplifies or attenuates the
transduced signal and sends it to a readout device as a
meter, digital readout, chart recorder, computer, etc.
 LIGHT SOURCES
Various UV radiation sources are as follows
a. Deuterium lamp
b. Hydrogen lamp
c. Tungsten lamp
d. Xenon discharge lamp
e. Mercury arc lamp

Various Visible radiation sources are as follow

a. Tungsten lamp
b. Mercury vapour lamp
c. Carbonone lamp
 Wavelength Selectors
 Wavelength selectors output a limited, narrow,
continuous group of wavelengths called a band.
Two types of wavelength selectors:
A) Filters
B) Monochromators

A)Filters –
Two types of filters:
a) Interference Filters
b) Absorption Filters
Cont..

B. Monochromators
 Wavelength selector that can continuously scan a
broad range of wavelengths.
 Used in most scanning spectrometers including UV,
visible, and IR instruments.
Refractive type
PRISM TYPE
Reflective type

Diffraction type
GRATING TYPE
Transmission Type
 SAMPLE COMPARTMENT
 Spectroscopy requires all materials in the beam path
other than the analyte should be as transparent to the
radiation as possible.
 The geometries of all components in the system should
be such as to maximize the signal and minimize the
scattered light.
 The material from which a sample cuvette is
fabricated controls the optical window that can be
used.
 Some typical materials are:
 Optical Glass - 335 - 2500 nm
 Special Optical Glass – 320 - 2500 nm
 Quartz (Infrared) – 220 - 3800 nm
 Quartz (Far-UV) – 170 - 2700 nm
 Detectors
 After the light has passed through the sample, we
want to be able to detect and measure the
resulting light.
 These types of detectors come in the form of
transducers that are able to take energy from light
and convert it into an electrical signal that can be
recorded, and if necessary, amplified.
 Three common types of detectors are used
 Barrier layer cells
 Photo emissive cell detector
 Photomultiplier
 SUMMARY
 Types of source, sample holder and detector for
various EM region

REGION SOURCE SAMPLE DETECTOR

HOLDER

Ultraviolet Deuterium lamp Quartz/Fused Phototube, PM

silica tube, diode array

Visible Tungsten lamp Glass/Quartz Phototube, PM

tube, diode array
 DIFFERENT UV-VISIBLE SPECTROPHOTOMETRIC
METHODS
FOR MULTICOMPONENT ANALYSIS

 (a) Simultaneous equation method

 (b) Absorbance ratio method
 (c) Derivative spectrophotometry
 (d)Difference spectrophotometry
(a) Simultaneous equation method:
 If a sample contains two absorbing drugs (X and Y) each of
which absorbs at the λ-max of the other (λ1 and λ2), it may
be possible to determine both the drugs by the
simultaneous equations method.
The information required is
 The absorptivities of X at λ1 and λ2, aX1 and aX2.
 The absorptivities of Y at λ1 and λ2, aY1 and aY2.
 The absorbances of the diluted sample at λ1 and λ2, A1 and
A2.

Let, Cx and Cy be the concentration of X and Y

respectively in the sample.

 The absorbance of the mixture is the sum of the individual

absorbances of X and Y
At λ1 A1 = aX1* Cx + aY1* Cy …………..(1)
At λ2 A2 = aX2* Cx + aY2* Cy …………..(2)
Multiply the equation (1) with aX2 and (2) with aX1
A1 aX2 = aX1 Cx aX2 + aY1 Cy aX2 …………(3)
A2 aX1 = aX2 Cx aX1+ aY2 Cy aX1 ………….(4)
A1 aX2 - A2 aX1 = aY1 Cy aX2 - aY2 Cy aX1
A1 aX2 - A2 aX1 = Cy (aY1 aX2 - aY2 aX1)
Cy = (A1 aX2 - A2 aX1) / (aY1 aX2 - aY2 aX1) ……….(5)
Same way we can derive
Cx = (A2 aY1 – A1 aY2) / (aY1 aX2 - aY2 aX1)………... (6)
These equations are known as simultaneous equations and by solving
these simultaneous equations we can determine the concentration of X
and Y in the sample.
(b) Absorbance ratio method:
The absorbance ratio method is a
modification of the simultaneous equations procedure.
In the quantitative assay of two components in
admixture by the absorbance ratio method, absorbances
are measured at two wavelengths, one being the λ-max of
one of the components (λ2) and other being a wavelength
of equal absorptivity of two components (λ1), i.e. an iso-
absorptive point.
 At λ1 A1 = aX1* Cx + aY1* Cy …………… (1)
 At λ2 A2 = aX2* Cx + aY2* Cy…………....(2)
Now divide (2) with (1)
A2/A1 = (aX2* Cx + aY2* Cy)/(aX1* Cx + aY1* Cy)
 Divide each term with (Cx + Cy)
A2/A1 = (aX2* Cx + aY2* Cy) / (Cx + Cy) (aX1* Cx + aY1* Cy) / (Cx + Cy)
Put Fx = Cx / (Cx + Cy) and Fy = Cy / (Cx + Cy)
A2/A1 = [aX2 Fx + aY2 Fy] / [aX1 Fx + aY1Fy]

Where Fx is the fraction of X and Fy is the fraction of Y i.e. Fy = 1-Fx

Therefore,
A2/A1 = [aX2 Fx + aY2 (1-Fx)] / [aX1 Fx + aY1(1-Fx)]
= [aX2 Fx + aY2 – aY2Fx] / [aX1 Fx + aY1 – aY1Fx]
At iso-absorptive point
aX1 = aY1 and Cx = Cy
There fore A2/A1 = [aX2 Fx + aY2 – aY2Fx] / aX1
= (aX2 Fx/ aX1) + (aY2/ aX1) –( aY2Fx/ aX1)
Let Qx = aX2/aX1 , Qy = aY2/aY1 and absorption ratio Qm = A2/A1
Qm = Fx Qx + Qy - Fx Qy
= Fx (Qx-Qy) + Qy
Fx = (Qm – Qy) / (Qx – Qy) ………………………..(3)
From the equations (1) A1 = aX1 (Cx + Cy)
there fore Cx + Cy = A1 / aX1
There fore Cx = (A1/aX1) – Cy ……………………(4)
From the equation (3)
Cx / (Cx + Cy) = (Qm – Qy) / (Qx – Qy)
There fore Cx / (A1 / aX1) = (Qm – Qy) / (Qx – Qy)
There fore Cx = [(Qm – Qy) / (Qx – Qy)] X (A1 / aX1) …………(5)
(e)Derivative Spectroscopy:
 For the purpose of spectral analysis in order to relate
chemical structure to electronic transitions, and for
analytical situations in which mixture contribute
interfering absorption, a method of manipulating the
spectral data is called derivative spectroscopy.
 Derivative spectrophotometry involves the conversions of a
normal spectrum to its first, second or higher derivative
spectrum. In the context of derivative spectrophotometry,
the normal absorption spectrum is referred to as the
fundamental, zero order, or D 0 spectrum.
 The first derivative D 1 spectrum is a plot of the rate of change of
absorbance with wavelength against wavelength i.e. a plot of the slope
of the fundamental spectrum against wavelength or a plot of dA/dλ vs.
λ. . The maximum positive and maximum negative slope respectively in
the D spectrum correspond with a maximum and a minimum
respectively in the D 1 spectrum. The λmax in D spectrum is a
wavelength of zero slope and gives dA/dλ = 0 in the D 1 spectrum.

 The second derivative D 2 spectrum is a plot of the curvature of the D

spectrum against wavelength or a plot of d 2 A/ dλ 2 vs. λ. The
maximum negative curvature in the D spectrum gives a minimum in
the D 2 spectrum, and the maximum positive curvature in the D
spectrum gives two small maxima called satellite bands in the D 2
spectrum. The wavelength of maximum slope and zero curvature in the
D spectrum correspond with cross-over points in the D 2 spectrum.
(f)Difference Spectroscopy:
 Difference spectroscopy provides a sensitive method for detecting
small changes in the environment of a chromophore or it can be used
to demonstrate ionization of a chromophore leading to identification
and quantitation of various components in a mixture.
The essential feature of a difference spectrophotometric assay
is that the measured value is the difference absorbance (Δ A) between
two equimolar solutions of the analyte in different forms which exhibit
different spectral characteristics.
 The criteria for applying difference spectrophotometry to the assay of a
substance in the presence of other absorbing substances are that:
A)Reproducible changes may be induced in the spectrum of the analyte
by the addition of one or more reagents.
B) The absorbance of the interfering substances is not altered by the
reagents.
 The simplest and most commonly employed technique for altering the
spectral properties of the analyte properties of the analyte is the
adjustment of the pH by means of aqueous solutions of acid, alkali or
buffers

A B
A)The Spectrum of compound in A(acid) and B(Base)
B) The difference spectrum of B relative to A
Conclusion:
 Qualitative & Quantitative Analysis:
 It is used for characterizing aromatic compounds and
conjugated olefins.
 It can be used to find out molar concentration of the
solute under study.
 Detection of impurities:
 It is one of the important method to detect impurities
in organic solvents.
 Detection of isomers are possible.
 Determination of molecular weight using Beer’s law.
Reference Books
 Introduction to Spectroscopy
 Donald A. Pavia
 Elementary Organic Spectroscopy
 Y. R. Sharma
 Practical Pharmaceutical Chemistry
 A.H. Beckett, J.B. Stenlake