Help in spectral elucidation

1. Structure elucidation of steroids
Presented to
Dr. Malik Saadullah
Presented by
Kanwal Irshad

2. Steroid
• Steroid is a biologically active organic
compound with four rings arranged in a
specific molecular configuration. Steroids have
cyclo pentanoperhydrophenanthreen rings.
• Steroid are hormone of three types
• Anabolic androgenic steroids
• Glucocorticosteroids
• Mineralocorticorsteroids

4. Ultraviolet Absorption Spectroscopy
• Organic compounds absorb UV radiation when
transition are induced between electronic
energy levels.
• Ttransition an interest in the present context
are mainly from ground state pi- orbitas to
unoccupied pi orbitals of higher energy.
• After undergoing electronic transition by the
absorption of photon of appropriate energy

5. • Chromophore
Any UV absorbing part of molecule is called a
chromophore., a term which extend and derived from
substances which absorb radiation in the visible region of
electromagnetic spectrum and appeared colored.
• Auxochrome
They are covalently bonded to saturated groups. These
when attached to a chromophore modifies the ability of
that chromophore to absorb light. They themselves fail to
produce color, but when present along with chromophore
in an organic compound intensifies the color of
chromogen.

6. • Electronic transition also occur in other groups
of organic compounds which have no
conjugated unsaturated systems, but the
spectra in such cases are of relatively little
practical value to organic chemist. They either
appear at wavelenght below 200 nm. (non-
conjugated unsaturated hydrocarbons)

7. Cholestrol

8. Interpretation of UV spectra
• Figure 1 shows the absorption spectra of the cholesterol
molecule in the spectral region 190–350 nm.
• Figure 2 shows a part of the absorption spectra in the
spectral region 225–350 nm.
• The strong and broad absorption peaks at 195 nm and 207
nm are seen (Fig. 1).
• This is in good agreement with the literature data since the
maximum absorbance of cholesterol has been reported
below 200 nm.
• Generally, if –C=C– bands are attached to one or two
tertiary carbon atoms, their absorption occurs at a slightly
longer wavelength (red shift) of about 200 nm.

9. Interpretation of UV spectra
• Thus, it may be concluded that the absorption peak
appeared at 207 nm is due the –C C– band present in
the cholesterol molecule.
• The other absorption peaks are also observed at 239
nm, 283 nm, and 294 nm in the spectrum (Fig. 2).
• The spectra (Figs. 2 and 3) clearly indicate that
cholesterol molecule gave indications of an extended
region of absorption on the ultra-violet side.
• No significant observable absorption peaks are seen
between 350–1400 nm.

10. UV spectra
Figure 1: UV-vis spectrum of Cholesterol.

11. Figure 2: A part of the UV-Vis spectrum of
cholesterol in the spectral region 225–350 nm.

12. Interpretation of IR spectra
• IR spectral peaks provide evidence of functional
groups in the sample.
• The analysis of IR spectra of steroids depends
upon the recognition of these peaks with
characteristics of structural features.
• Most of useful absorption bands lie above 1500
cm-1. These called fingerprint region of the
spectrum, below, 1500 cm-1, invariably contains
many peaks that cannot be assigned to specific
vibrations.

13. • Two or more electronegative atoms on the
same carbon atom as the proton cause larger
chemical shifts.

15. • The strenght of absorption band depends
upon the magnitude of dipole associated with
particular vibrating groups; only those
structural features whose vibrations involve
significant change in the band dipole are able
to interact with IR radiations. The strongest
absorption bands therefore result from 0-H,
C=O, and other highly polarized bonds.

16. • The major bands identified for cholesterol
molecule were found at 3400, 2866, 1674, 1512,
1464, 1438, 1178, 840, and 800 cm−1.
• The bands between 2800–3000 cm−1 are
characterized due to asymmetric and symmetric
stretching vibrations of CH2and CH3 groups.
• The observed broad and intense band nearly at
3400 cm−1 is attributed to OH stretching.
• The characteristic strong peak at 2899 cm−1 is due
to CH2 symmetric stretching vibration.
• Cholesterol has one double band (C=C) in the
second ring. This was prominently shown at 1674
cm−1.

17. • The band at 1438 cm−1 is due to deformation
vibrations of CH2and CH3 groups.
• The band at 1170 cm−1 is due to the CH
bending of cholesterol molecule.
• The bands between 900–675 cm−1 are
characterized due the C-H out-of-plane
bending which are the characteristic of the
aromatic substitution pattern.

20. Nuclear magnetic resonance
spectroscopy
• An NMR instrument allows the molecular
structure of a material to be analyzed by
observing and measuring the interaction of
nuclear spins when placed in a powerful
magnetic field.

27. Mass spectrum of chloestrol