UV-visible spectroscopy involves using electromagnetic radiation in the ultraviolet-visible spectral region to analyze chemical substances. It works by measuring how molecules absorb different wavelengths of visible and ultraviolet light. There are several techniques covered in the document, including UV-visible spectroscopy which analyzes electronic transitions in bonding electrons, and how it can be used to determine structural properties like conjugation and stereochemistry based on wavelength absorption maximum values. The document also outlines other spectroscopic techniques like infrared and NMR spectroscopy.

1. UV Visible spectroscopy
By
Mr. G. P. Sadawarte
Asst. Professor,Dept. of Chemistry
B. P. Arts, S.M.A. Sci. and K.K.C. Comm. College
chalisgaon
B.P. Arts, S.M.A. Science And K.K.C.
Commerce College, Chalisgaon,

2. Spectroscopy
WHAT IS SPECTROSCOPY?
The study of the interaction between
ELECTROMAGNETIC (EM) RADIATION and MATTER

3. Wave parameter
Frequency (V) – the number of cycles/wave which pass a
fixed point in space per second.
Amplitude (A) – The maximum length of the electric vector
in the wave from X axis (Maximum height of a wave).
Wavelength (λ) – The distance between two successive
crest/troughs adjacent points in a wave (usually maxima or
minima).
Wavenumber- The number of waves per cm in units of cm-1.

4. Energy
• EM is viewed as a stream of discrete particles, or wave
packets, of energy called photons.
• We can relate the energy of photon to its wavelength,
frequency and wavenumber by
E = hV V - frequency
= h c
λ λ - wavelength
= hcυ
h – Planck’s constant =6.63x10-34 J·s
Energy inversely proportional to Wavelength

5. Electromagnetic Spectrum
Region Wavelength Range
UV 180 – 380 nm
Visible 380 – 780 nm

6. Spectroscopic Techniques and
Chemistry they Probe
UV-vis UV-vis region bonding electrons
Atomic Absorption UV-vis region atomic transitions (val. e-)
FT-IR IR/Microwave vibrations, rotations
Raman IR/UV vibrations
FT-NMR Radio waves nuclear spin states
X-Ray Spectroscopy X-rays inner electrons, elemental
X-ray Crystallography X-rays 3-D structure

7. Different Spectroscopies
• UV-vis – electronic states of valence e/d-orbital
transitions for solvated transition metals
• Fluorescence – emission of UV/vis by certain molecules
• FT-IR – vibrational transitions of molecules
• FT-NMR – nuclear spin transitions
• X-Ray Spectroscopy – electronic transitions of core
electrons

8. Molecular transition
• In molecules the electronic states are subdivided into
vibrational states.
• The energy of a band in a molecular absorption
spectrum is the sum of three different energy
components.
• E = Eelectronic + Evibrational + Erotational
• Transitions between electronic-vibrational-rotational
states give rise to spectra that appear to have bands.

9. Lambert Beer’s Law
cuvette
source
slit
detector
log(I0/I) = ϵ.l.c
I0 = intensity of incident light
I = intensity of Transmitted light
c = Concentration of sample
l = Path length of sample
ϵ = Molar absorptivity
The fraction of incident
light absorbed is
proportional to no of
absorbing molecule in its
path

10. Light source and detector
REGION SOURCE SAMPLE
HOLDER
DETECTOR
Ultraviolet Deuterium lamp Quartz/fused
silica
Phototube, PM
tube, diode array
Visible Tungsten lamp Glass/quartz Phototube, PM
tube, diode array
Infrared Nernst glower (rare earth
oxides or silicon carbide
glowers)
Salt crystals e.g.
crystalline
sodium chloride
Thermocouples,
bolometers

11. Electronic transition

12. Chromophore
• Unsaturated group
• C=C, C=O, C=N,
• 100 to 400 nm
Benzene (255 nm)
H
H H
H
Ethylene(170 nm)

13. Auxochrome
• Saturated functional group which does not
absorbs UV radiation at longer wavelength.
• When its is connected to Chromophore it
changes both wavelength and intensity
• OH, NH2, Cl,
Benzene (255 nm)
OH
Phenol (270 nm)
NH2
Aniline (280 nm)

14. Bathochromic shift
• Shift in absorption to longer wavelength
• Red shift
• ˄ max increses
OH
• Phenol (270nm) • Phenoxide ion (287 nm)
O
P Nitro phenol (320) and Phenoxide of it (400)

15. Hypsochromic Shift
• Shift in absorption to shorter wavelength
• Blue shift
• ˄ max decreases
Aniline (280nm ) Aniline hydrochloride (203 nm)
NH2
NH3Cl

16. Woodward Fischer Rule
• Homoannular Diene -Both double bonds are
conjugation in same ring
• S-cis or cisoid
• Base value ʎ max 253 nm

17. Woodward Fischer Rule
• Heteroannular Diene-double bonds are in
conjugation Present two different ring
• S-Trans or Transoid
• Base value ʎ max 215 nm
Heteroannular

18. Woodward Fischer Rule
Exocyclic double bond
Double bond projected to outside ring Add 5 nm
For each Alkyl Substituent or Ring residue add 5 nm
Extra DB Which increases Conjugation =30 nm
Exocyclic DB

19. Woodward Fischer Rule

20. Problems Calculation of λmax- diene system

21. Problems Calculation of λmax- diene system

22. Problems Calculation of λmax- diene system

23. Problems Calculation of λmax- diene system

24. Woodward Fischer Rule –enone system
• Base value for cyclic/ six membered enone 215nm
• Base value for cyclic Five membered enone 202nm
• Base value for aldehyde 207nm
• Base value for acid /ester 197nm
• Extra DB which increases Conjugation 30 nm
• Homodiene Componant 39 nm
• Exocyclic DB 05nm

25. Woodward Fischer Rule –enone system
Group Alpha Beta Gamma Delta Other Than
Delta
Alkyl 10 12 18 18 18
OR 35 30 17 31 --
OH 35 30 30 50 --
Cl 15 12 12 12 --
Br 25 30 25 25 --
OCOR 06 06 06 06 --
amino -- 95 -- -- --
SR -- 80 -- -- --

26. Problems Calculation of λmax- Eneone system
H3C
H
C
C
H
C
CH3
O
O
HO

27. O
CH3
O
Problems Calculation of λmax- eneone system

28. Problems Calculation of λmax- eneone system
O
CH3

29. Application of UV Visible
• Structure determination – presence or absence of
Chromophore and Conjugation
• Determination of steriochemistry-
Cis stilbene λ Max 280nm
Trans stilbene λ max 296nm
• Strength of Hydrogen Bond –
Acetone in n-Hexane 297nm
Acetone in water 264nm

30. References
• Introduction to Spectroscopy, Donald L. Pavia Gary
M. Lampman George S. Kriz James R. Vyvyan,
• Spectroscopy by Y.R. Sharma
• Spectrometric Identification of Organic
Compounds, R. M. Silverstein and F. X. Webster ,
John Wiley and Sons

31. Any ?