ESR line shape studies of N (4-n butyl benzilidine) 4-amino 2,2,6,6-tetramethyl piperidine 1-oxide (BBTMPO) in toluene

Article abstract of DOI:10.1063/1.450603

BBTMPO was synthesized by a condensation of 4-n butyl benzaldehyde and 4-amino 2,2,6,6- tetramethyl piperidine N oxide (4-tempamine).The shape of the resulting spin probe, estimated using the Dreiding models, is a spherocone of length 10.7 Angstroem capped by hemispheres of radii 6.6 and 4.0 Angstroem, respectively.The magnetic parameters of BBTMPO in toluene at 77 K were determined.Variable temperature ESR line shape studies in the temperature range of 142-211 K revealed that BBTMPO exhibited anisotropic rotational ditFusion in toluene along the long axis of the spherocone and in the direction parallel to the N-O bond.Rotational diffusion along the long axis was found to be 3+/-0.5 and 7+/-0.5 times faster for frozen and liquid toluene, respectively, than the other two axes.The line shapes have been simulated by using the stochastic Liouville theory of slow-motional effects on ESR spectrum.The slow tumbling spectrum (158 K) in the model-sensitive region showed good agreement for a Brownian model.The plot of τ_R vs 1/T over the whole temperature range yield a good linear fit with two slopes, with the activation energy for reorientation process of 4.9 kcal/mol in the liquid state, and 9.9 kcal/mol in the solid state.The higher activation energy of rotational reorientation coupled with a lower anisotropy of molecular reorientation (N) in the solid state, indicates that the rotational degrees of freedom is more restricted in the frozen state than in the liquid state.Molecular reorientation for BBTMPO in toluene was analyzed in terms of the hydrodynamic free space model for molecular relaxation in liquids.The stickiness factor S was found to be 0.6 while the anisotropic interaction parameter K which measures the coupling of rotation to translation was found to be 0.7.For perdeuterated 2,2,6,6-tetramethyl-4-piperidine N-oxide (PD-Tempone) in toluene the stickiness factor was calculated to be 0.3, and κ was 0.4.The doubling in size and weight in going from PD-Tempone to BBTMPO increases the stickiness factor and K from 0.3 to 0.6, and 0.4 to 0.7, respectively.The similarity in the structure of BBTMPO to that of liquid crystal methoxy benzilidine butyl aniline (MBBA) and its potential use as a spin probe for MBBA is discussed.

Full text of DOI:10.1063/1.450603

ESR line shape studies of N(4n butyl benzilidine) 4amino 2,2,6,6tetramethyl
piperidine 1oxide (BBTMPO) in toluene
J. S. Hwang, P. Pollet, and M. M. Saleem
Citation: The Journal of Chemical Physics 84, 577 (1986); doi: 10.1063/1.450603
View online: http://dx.doi.org/10.1063/1.450603
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/84/2?ver=pdfcov
Published by the AIP Publishing
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This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
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This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
136.165.238.131 On: Fri, 19 Dec 2014 14:21:13

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
136.165.238.131 On: Fri, 19 Dec 2014 14:21:13

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
136.165.238.131 On: Fri, 19 Dec 2014 14:21:13

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
136.165.238.131 On: Fri, 19 Dec 2014 14:21:13

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
136.165.238.131 On: Fri, 19 Dec 2014 14:21:13

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
136.165.238.131 On: Fri, 19 Dec 2014 14:21:13