Solvent dependence of rotational anisotropy and molecular geometry as probed by NMR cross-relaxation rates O. Walker a , P. Mutzenhardt a, * , J.P. Joly b , D. Canet a,1 a Laboratoire de M ethodologie RMN, Faculte des Sciences, Universit e Henri Poincar e, Nancy 1, UPRESA CNRS 7049 FR CNRS 1742, BP 239, F-54506 Vandoeuvre-l  es-Nancy Cedex, France b Groupe SUCRES, UMR-CNRS 7565, Structure et R eactivit e des Syst  emes Mol eculaires Complexes, Facult e des Sciences, Universit e Henri Poincar e, Nancy 1, INCM-FR CNRS 1742, BP 239, F-54506 Vandoeuvre-l  es-Nancy Cedex, France Received 18 January 2002; in final form 14 March 2002 Abstract A medium size and rigid molecule (2,3-naphto-1,3-dioxole) has been selected for this study because full anisotropic reorientation is expected and because its symmetry elements dictate the orientation of the rotation–diffusion tensor. NMR measurements include direct cross-relaxation rates (which yield the three rotation–diffusion coefficients by as- suming the length of CH bonds) and remote cross-relaxation rates (which, by using these rotation–diffusion coefficients, yield distances between a given carbon and remote protons). Two different solvents have been used: carbon disulfide and dimethyl sulfoxide. In both solvents, the same type of reorientation anisotropy is observed although with different ratios of rotation–diffusion coefficient values, presumably due to specific intermolecular interactions undergone by the dioxole ring. This would also explain geometrical variations at the level of this moiety. Ó 2002 Published by Elsevier Science B.V. It has been shown previously [1] that in rigid molecules, heteronuclear ( 13 C– 1 H) cross-relaxation rates can provide accurate information about re- orientational anisotropy and, in a second step, distances between a given carbon and proton(s) non-directly bonded to this carbon. The method rests on the quantitative measurement of cross-re- laxation rates by the so-called heteronuclear Overhauser effect spectroscopy (HOESY) [2] two- dimensional NMR experiment. Methodological aspects have been given before [1] and will just be briefly recalled: the experiment starts with an evo- lution period (which provides proton chemical shift labeling), followed by a mixing time which allows for magnetization build-up by cross-relaxation (this process is called nuclear Overhauser effect (nOe) [3] and ends by carbon-13 detection. Cross-peaks, in the relevant two-dimensional spectrum, are thus representative of nOe’s within a ( 13 C; 1 H) pair in- volving a non-negligible dipolar interaction (it can be reminded that cross-relaxation depends exclu- sively on dipolar interactions, see below). In that way, one usually observes cross-peaks with directly bonded proton(s) but also with remote proton(s). A particular point of the sequence used in this work is 3 May 2002 Chemical Physics Letters 357 (2002) 103–107 www.elsevier.com/locate/cplett * Corresponding author. Fax: +33-383-91-23-67. E-mail addresses: daniel.canet@rmn.uhp-nancy.fr (O. Walk- er), pierre.mutzenhardt@rmn.uhp-nancy.fr (P. Mutzenhardt). 1 Also corresponding author. 0009-2614/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII:S0009-2614(02)00449-9