Factor Analysis as a Complement to Band Resolution Techniques. III. Self Association in Trichloroacetic Acid

1975 ◽  
Vol 53 (9) ◽  
pp. 1251-1257 ◽  
Author(s):  
J. T. Bulmer ◽  
H. F. Shurvell
Keyword(s):  
Factor Analysis ◽  
Infrared Spectra ◽  
Trichloroacetic Acid ◽  
Linear Polymers ◽  
Carbonyl Groups ◽  
Absorption Coefficients ◽  
Average Value ◽  
Self Association ◽  
Shape Ratio ◽  
Monomer Band

Digitized infrared spectra of nine solutions of trichloroacetic acid in CCl4 have been studied in the carbonyl stretching region. At all concentrations only two bands are visually apparent. However, factor analysis indicates the presence of four absorbing components. The contour resolution technique gives a monomer band at 1786 cm−1, a dimer band at 1749 cm−1, and a third band close to the dimer frequency at approximately 1735 cm−1. Examination of the changes in Cauchy–Gauss shape ratio of the monomer band with increasing concentration indicates the presence of an unresolved component. The band at 1735 cm−1 and the unresolved band near the monomer peak at 1786 cm−1 are assigned to absorption of carbonyl groups in linear polymers of trichloroaceticacid. The monomer–dimer equilibrium constant was calculated from the molar absorption coefficients and absorbances of monomer and dimer bands. The average value over the concentration range 0.305 × 10−3 to 0.1603 M was 287 l/mol at 33.9 ± 0.5 °C.

PROTONATED CARBONYL GROUPS: IV. N,N-DIMETHYLACETAMIDE SALTS

1964 ◽  
Vol 42 (12) ◽  
pp. 2721-2727 ◽  
Author(s):  
Denys Cook
Keyword(s):  
Oxygen Atom ◽  
Infrared Spectra ◽  
Deformation Mode ◽  
Carbonyl Groups ◽  
Broad Absorption ◽  
Average Value ◽  
Correlation Field ◽  
Bending Mode ◽  
Out Of Plane ◽  
Transmission Windows

The infrared spectra of N,N-dimethylacelamide salts have been recorded and are consistent with protonation at the oxygen atom, vOH is between 2 095 and 3 360 cm−1 depending on the anion. The average value of the two components of the OH in-plane hydrogen-bending mode, δOH, is 1 253 cm−1 (splitting of about 147 cm−1 due to correlation field effects). The out-of-plane hydrogen-deformation mode occurs at 928 to 761 cm−1 depending on the salt. The 1 680 and 1 400 cm−1 bands which are present in all the salts are associated chiefly with stretching the CN and CO bonds respectively, in the OCN group, though it is likely that the vibrations are somewhat mixed.Some salts of complex acids are of the 2 base: 1 acid variety with very strong broad absorption centered near 900 cm−1, containing sharp transmission windows.

Stereospecific Association of C-20 Epimers of 3β-Hydroxy-16-oxo-24-nor-17-azachol-5-eno-23-nitryle

1997 ◽  
Vol 52 (6) ◽  
pp. 749-756
Author(s):  
Zofia Plesnar ◽  
Stanisław Malanowski ◽  
Zenon Lotowski ◽  
Jacek W. Morzycki ◽  
Jadwiga Frelek ◽  
...  
Keyword(s):  
Proton Nuclear Magnetic Resonance ◽  
Side Chain ◽  
Water Molecules ◽  
Carbonyl Groups ◽  
Nmr Data ◽  
Molecular Modelling Studies ◽  
Modelling Studies ◽  
Lactam Carbonyl ◽  
Self Association ◽  
Chain Conformations

Abstract The cryoscopic measurements show that title compounds are strongly associated in CHCl3 solutions. The association of the 20 R epimer is distinctly less pronounced than that of the 20 S epipmer. Self-association of the 20 S epimer leads to the formation of very large com­plexes. The 20 R epimer forms associates via water molecules. The dissimilarity may be ex­plained in terms of different accessibility of the lactam carbonyl groups in the two epimers for the association. It is proposed that the association process is controlled by the configura­tion at the carbon atom C(20) and conformation around the C(20)-C(22) bond. Populations of side chain conformations of both epimers were determined by means of proton nuclear magnetic resonance. It was found for the 20 R epimer that the t and the -g rotamers are almost equally populated, and the rotamer +g is excluded. For the 20 S epimer the +g rotamer predominates over the t one, and the -g rotamer is excluded. The NMR data are fully consistent with the results of the molecular modelling studies.

The Effects of Modulation on an RF Discharge in Silane and on the Deposited a-Si:H

1987 ◽  
Vol 98 ◽  
Author(s):  
L. J. Overzet ◽  
J. T. Verdeyen ◽  
R. M. Roth ◽  
F. F. Carasco
Keyword(s):  
Electron Density ◽  
Average Power ◽  
Optical Emission ◽  
Rf Discharge ◽  
Absorption Coefficients ◽  
Average Value ◽  
Optical Bandgaps ◽  
Time Average ◽  
Substrate Temperatures ◽  
Attachment Process

ABSTRACTThe time evolution of the electron density and the optical emission intensity in response to a square wave modulated RF excitation of helium-silane mixtures has been studied and compared to that for the more conventional CW discharge. In addition, the films deposited from CW and modulated RF glows have-been compared on the basis of absorption coefficients and photoconductivities. Films deposited from modulated glows at substrate temperatures below 200°C have significantly smaller optical bandgaps than those deposited from comparable CW discharges. The bulk electron density in the modulated discharge undergoes a complex temporal variation and its time average value can be significantly larger than that in the CW glow despite the lower average power. A dissociative attachment process involving silane radicals, SiHn (n = 1 to 3), is identified as the most probable cause.

Use of spherical projections in factor analysis of mid-infrared spectra of mixtures

1994 ◽  
Vol 31 (7) ◽  
pp. 205
Author(s):  
Stephen P. Gurden ◽  
Richard G. Brereton ◽  
John A. Groves
Keyword(s):  
Factor Analysis ◽  
Infrared Spectra ◽  
Mid Infrared

Effect of the chain length on near-infrared spectra of 1-alcohols from methanol to 1-decanol

NIR news ◽  
2019 ◽  
Vol 30 (3) ◽  
pp. 6-8
Author(s):  
Mirosław Antoni Czarnecki ◽  
Michał Kwaśniewicz
Keyword(s):  
Principal Component Analysis ◽  
Chain Length ◽  
Infrared Spectra ◽  
Near Infrared ◽  
Principal Component ◽  
Pure Liquid ◽  
Chemometric Methods ◽  
Near Infrared Spectra ◽  
Similarities And Differences ◽  
Self Association

This work shows the effect of the chain length on near-infrared spectra of 1-alcohols and is based on a recent paper by Kwaśniewicz and Czarnecki ( Appl Spectrosc 2018, 72: 288). Near-infrared spectra of 1-alcohols from methanol to 1-decanol in the pure liquid phase were recorded from 5200 to 9000 cm−1. The similarities and differences between the spectra were analyzed by the classical and chemometric methods (principal component analysis). The obtained results reveal that the near-infrared spectra of methanol, ethanol, and 1-propanol are appreciably different from the spectra of higher 1-alcohols. As shown, the degree of self-association of 1-alcohols decreases with the increase in the chain length.

Deuterium isotope effects and assignment of 13C chemical shifts in spectra of methyl octadecanoate and the sixteen isomeric oxooctadecanoates

1977 ◽  
Vol 55 (7) ◽  
pp. 1135-1142 ◽  
Author(s):  
A. P. Tulloch
Keyword(s):  
Chemical Shifts ◽  
Isotope Effects ◽  
Carbonyl Groups ◽  
Average Value ◽  
Fatty Acid Chain ◽  
Methylene Groups ◽  
Deuterium Isotope Effects ◽  
Methyl Octadecanoate ◽  
Atom Effect ◽  
C Nmr

13C nmr spectra of the 16 isomeric gem-dideuterooctadecanoates were measured and second and third atom deuterium isotope effects calculated for most of the affected carbons of 12 of the isomers. The average value for the second atom effect was −0.20 ppm and for the third atom effect was −0.05 ppm. From these effects and the changes in spectra caused by introduction of two deuterons at positions along the fatty acid chain, chemical shifts were determined for all carbons of methyl octadecanoate. Spectra of seven dideuterooxooctadecanoates, with both deuterons attached to a carbon γ to the oxo group, were measured, and using isotope effects, unambiguous assignments of chemical shift were made. Chemical shifts were thus assigned to all carbons in the 16 isomeric oxooctadecanoates and these show the effect of the carbonyl group at different positions in the chain. The results indicate that, in addition to large effects on carbons α and β to the oxo group, the γ to θ carbons are all shielded with displacements: γ −0.46, δ −0.30, ε −0.27, ζ −0.13, η −0.09, and θ −0.06 ppm. The effects of the oxo and ester carbonyls extend over seven methylene groups, but shielding due to ester carbonyl is a little smaller. Spectra of 2- to 9-oxo esters showed that interaction between the two carbonyl groups causes relatively greater shielding of carbons situated between the groups.

A Low Temperature Infrared Study of Self-association in Thiols

1972 ◽  
Vol 50 (22) ◽  
pp. 3594-3600 ◽  
Author(s):  
R. Bicca de Alencastro ◽  
C. Sandorfy
Keyword(s):  
Hydrogen Bonding ◽  
Low Temperature ◽  
Infrared Spectra ◽  
Low Temperatures ◽  
Infrared Study ◽  
Text Type ◽  
Stretching Vibration ◽  
Aliphatic Thiols ◽  
Self Association ◽  
Associated Species

The infrared spectra of several aliphatic thiols and of benzenethiol were measured between 2400 and 2700 cm−1, and 4800 and 5300 cm−1 in a 1:1 mixture of CCl3F and C2F4Br2, at temperatures ranging from 20 to −190 °C. Dimerization takes place at low temperatures and more highly associated species also appear. Free S—H groups are present in the solutions as well as in the pure liquids, even at the lowest temperatures. The association is of the [Formula: see text] type in aliphatic thiols; both [Formula: see text] and [Formula: see text] bonds are found in the case of benzenethiol and α-toluenethiol. Hydrogen bonding has little effect on the anharmonicity of the S—H stretching vibration.

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