Diapositiva 1

1
LXNMR_S.C.An. Determinazione di distanze e
angoli di legame in fasi liquid-like.
Relatore Dr. Giuseppe Pileio (Ph.D. student
STM3)
2
This talk will deal with
3
A model to treat vibrational motions
Using cartesian notation and supposing no
vibro-rotational coupling, dipolar coupling may
be expressed by
r
re
Being re the equilibrium distance and r the
istantaneous excursion of r from re we may
approximate
and dipolar couplings
Eigenvectors and Eigenvalues of Force Field
Matrix.
e, a, h mean equilibrium, anharmonic and harmonic
For furher informations S. S?kora, J. Vogt, H.
Bösiger and P. Diehl, J. Magn. Reson., (1979),
36, 53-60
4
The problem of the Force Field quality
For rigid molecules accuracy of 10-4 Å for bond
lengths and 10-1 degree for angles can be
achieved
Spectrum with narrow linewidth and high S/N ratio
5
What are we searching for?
High simmetry, 2 parameters vs 7 Dij
A reliable experimental Force Field exists1
1 J. R. Scherer, Spectrochim. Acta, (1964), 20,
345-358 and (1967), 23A, 1489-1497
2 P. Diehl, H. Bsinger and H. Zimmermann, J.
Magn. Reson., (1979), 33, 113-126
6
What is the best theoretical method to calculate
Force Field
Normal Modes and IR frequencies both
calculated with G98W
- - 6.3 . 10-4
55
1.08089
1.08026
Normal Modes calculated with G98W but
Experimental Frequencies
- 1.0 . 10-5
33
The best set of dh seems the one calculated with
Normal Modes by B3LYP and experimental
frequencies
1.08026
1.08025
7
The problem of the Satellites spectra
Lines of 13C-proton satellite spectra are lost at
the bottom of the proton lines since their
intensity is about 100 times smaller.

• Then, 13C-proton satellite spectral analysis is
  very difficult
• many lines are lost in the noise
• many lines are lost inside the 1H transitions
• transitions from different satellites overlap

Accuracy on determination of Dijs became
smaller.
8
?rab is rmax rmin from 100 runs varying the Dij
within their standard deviations
The accuracy of spectral analysis may be crucial
(spreading of 10-2)
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What is the influence of the Spectral Analysis on
geometrical parameters?
DCH are determined with an accuracy about an
order of magnitude lower than the relative
obtained from the analysis of the 13C enriched
sample.
The spreading on rCH is an order of magnitude
higher when dealing with satellite in natural
abundance
?rCH is rmax rmin from 100 runs varying the Dij
within their standard deviations
The neglected contribution are of the order of
10-4 but in I35 an order of magnitude higher
?(a/b) / 104 (ra/rb)cal (ra/rb)hex /
(ra/rb)hex
10
LXNMR_S.C.An. Group
Prof. Marcello Longeri
Prof. Giorgio Celebre
tesisti
Dr. Giuseppina De Luca
Maiorino Michela De Lorenzo Luana Concistrè Maria
Dr. Giuseppe Pileio
The End
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VynilBromide dissolved in CCN-55 13C2 proton
satellite spectrum.
calculated
experimental