ATENOLOL - INFRA-RED, MASS SPECTRA, 1-HYDROGEN NMR, 13-CARBON NMR

SPECTROSCOPY

In order for one to appreciate the spectroscopy for ATENOLOL, one must initially consider its full molecular structure. The simplest means to explore and trace the ATENOLOL's spectroscopic characteristics is to look at its 2D arrangement :

On the outset it is clear that ATENOLOL possesses a multitude of component substituents. The main "bulk" on the molecule is attached to a bulky structure itself, namely the benzene ring. As hinted on the homepage, such a molecule can be described as a benzeneacetamide by virtue of the O=C-NH2 amide group extruding from a benzene ring. As well as the amide functional group, the conjugating C=C bond in the benzene ring, the methine (CH), methylene (CH2), methyl (CH3) and -OH functional group should be distinctive on the IR spectra (amide circa 1650cm-1 ; CH circa 2880-2900cm-1 ; CH2 circa 2916-2936 cm-1 ; CH3 circa 2850 cm-1 ; conjugating C=C circa 1640-1610 ; -OH circa 3200-3550cm-1). The mass spectra should theoretically present the molecular ion at 266, being the relative molecular mass of the drug. In relation to ATENOLOL's 13-Carbon and 1-Hydrogen nmr, the splitting patterns would be vast, likely to have one pronounced broad peak due to the -OH group. The effect of the electronegative oxygen leads to neighbouring hydrogen nuclei being deshielded, moving the coupling peaks downfield whilst also possibly giving rise to hydrogen bonding. The predictions will now be tested, utilising the 2D structure above to explain the various observations which prevail...

IR SPECTRA

INFRA RED SPECTRA OF ATENOLOL CONDUCTED ON A KBR DISC

IR FREQUENCY BAND (cm-1)
GROUP RESPONSIBLE
3368
-OH
3198-3071
H-N
2966
C-CH3
2924
CH2
2870
C-H
1666
C=O
1649
O=C-NH2
1614
Conjugated C=C (aromatic)
886
C=CH2

A key observation which is raised in the IR spectrum of ATENOLOL is the level of hydrogen bonding. By virtue of the electronegative Nitrogen atom and the even more electronegative Oxygen atom, the IR spectra indicates that intermolecular H-bonding may be present. This is demonstrated by the IR frequency bands of the -OH and H-N and groups having stretched at 3368cm-1 and 3198-3071 cm-1 respectively. Theoretical values indicate the following ; (a "free" group representing a non H-bonded group) :

IR FREQUENCY BAND (cm-1)
GROUP RESPONSIBLE
3610-3645 (sharp)
Free -OH
3200-3550 (broad)
H bonded -OH
3300-3500
Free -NH
3070-3350
H bonded NH

By simply cross referencing these figures with those obtained from the IR spectrum one is able to establish that hydrogen-bonding is present, as hypothesised in our prediction at the beginning of the section.

MASS SPECTRA

MASS SPECTRA OF ATENOLOL

Source Temperature: 160 C
Sample Temperature: 140 C
Direct, 75 eV

A TABLE OF THE RESPONSIBLE STRUCTURAL FRAGMETS

m/z
Structural Fragment
266
251
222
134
72
58
44
28

The molecular ion was determined at 266, as predicted. The array of fragments tabulated above encapsulate the diversity of component constituents which structure the ATENOLOL molecule.

1-HYDROGEN NMR

1-H NMR OF ATENOLOL

CONDUCTED @ 399.65 MHz
0.039 g : 0.5 ml CDCl3

Proton
Chemical Shift (ppm)
a
7.41
b
7.158
c
6.855
d
3.84
e
5.00
f
3.91
g
2.539
h
1.50
i
2.68
j
0.970
k
0.975
l
6.85
m
3.285

There are a few key inferences that can be made from the data acquired. Proton a is bonded to Nitrogen, a fairly potent electronegative atom (3.04 Pauling units). The N-H bond is thus slightly polarised with the Nitrogen atom drawing the hydrogen's electron towards it. The nature of this bond means that Proton a becomes deshielded thereby making it extremely acidic. The net effect is that the 1-H nmr displays the proton vastly downfield in relation to its counterparts. For comparative purposes, it is clear that Proton's j and k are shielded rather well by virtue of their extreme upfield positions. They exhibit integration, being in the same environment shown as the largest peak on the spectra. As well as Proton a, Proton c experiences deshielding even though not being directly bonded to the electronegative species. The atom responsible is now the extremely electronegative Oxygen atom (3.44 Pauling units). Despite its distance, the pair of protons experience deshielding by virtue of oxygen's potent electron withdrawing affect. As predicted, Proton e is isolated as a single broad peak not coupling with neighbouring atoms, being attached to the electronegative Oxygen atom. Coupling is displayed, pronounced for Protons i whereby it is able to couple with Protons k and j, evolving a doublet of quartets.

13-CARBON NMR

13-C NMR OF ATENOLOL

CONDUCTED @ 22.53 MHz
0.039 g : 0.5 ml DMSO-d6

Carbon
Chemical Shift (ppm)
Intensity
1
172.52
366
2
157.27
440
3
129.88
967
4
128.31
477
5
114.17
946
6
70.81
361
7
68.35
478
8
49.96
394
9
48.09
553
10
41.31
285
11
22.88
1000

Similar inferences can be made for the 13-Carbon nmr, with the electronegative oxygen showing obvious electronegative potency with Carbon 1 being shifted extremely downfield this time being assisted with the largely electronegative Nitrogen atom as well. The net effect is a highly polarised delta positive carbon atom.

THE SCOPE OF...SCOPY

 
 

 

MOLECULAR

SPECTROSCOPY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Home      Imperial College     Acknowledgements      Contact     Disclaimer
Copyright 2004 Ravi Bhandari. All rights reserved.