Five-Membered Ring Rotations, Pseudorotations, and Hydrogen Bond Exchange Dynamics in the Solid State Studied by NMR Spectroscopy

Abstract

13C CP/MAS NMR studies were carried out on trans-1,2-cyclopentanediol, on 4,4-dimethyl-trans-1,2-cyclopentanediol, and on sulfolane at variable temperatures. The spectra showed evidence of three dynamic solid-state processes: hydrogen bond exchange, ring pseudorotation, and whole molecule rotations about local C 2 axes. Fitting of T 1 ρ data to calculated values of the 13C−1H dipolar interactions allowed differentiation between ring pseudorotations and whole molecule C 2 reorientations. Isotopic 1H/2H substitution demonstrated the existence of hydrogen bond exchange processes in the diols. Activation parameters for these processes were derived from both coalescence measurements and the T 1 ρ measurements.

Mechanisms and Beyond: Elucidation of Fluxional Dynamics by Exchange NMR Spectroscopy

“…The dissociation barrier was 17.5 kcal mol −1 at 22 °C. Related studies on intramolecular small molecule hydrogen bond exchange have been carried out by Riddel's group on both o ‐vanillin salicyloyl hydrazone and MAS 1 H‐ 1 H EXSY of trans ‐1,2‐cyclopentanediols …”

“…Urea 73 forms "tennis ball" dimer 74 capableo fm olecular encapsulation of guest molecules ;h ydrogen bonding was examined by using trisaccharide 75. change have been carried out by Riddel's group on both ovanillin salicyloyl hydrazone [120] and MAS 1 H-1 HE XSY of trans-1,2-cyclopentanediols. [121] 1 H-1 HE XSY wasu sed to study the intermolecularh ydrogenbondingi nteractions of trisaccharide 75. [122] By adding H 2 Ot o the NMR sample and using aw ater suppressionp ulse sequence, chemical exchange could be seen between water and hydroxyl protons on the sugar.I nvestigations into the oligosaccharide anticoagulant drug Atrixa [123] showed chemical exchange betweenh ydroxy protons on the sugar and in water.…”

Models for molecular motions within polymer chains. Part 1. A solid-state NMR study of hexane-1,6-diyl bis( p-nitrobenzoate)

“…In principle, values of the 13 C-1 H dipolar interaction B 2 can be interpreted in terms of particular modes of motion. 21 In the absence of this information the 13 C T 1ρ data provide no indication of the mode of the motion although they provide an estimate of the energy of activation. To obtain information on the motions involved other NMR methods must be applied.…”

“…These studies should be considered as following from our earlier studies of molecular motions in crystalline solids using CP/MAS techniques. [17][18][19][20][21] In very general terms there are two types of chain that we should be concerned with: those in which the consecutive C-C bonds are arranged all trans and those in which there are some bonds that are gauche. For examples of the first category we examined the straight chain dicarboxylic acids in the series succinic to suberic acid.…”

Conformation and hydrogen bonding for the bicyclic compound 3-thiabicyclo[3.2.0]heptane-6,7-dicarboxylic acid 3,3-dioxide

“…Cyclopentane and substituted cyclopentane rings are nonplanar, with two low-energy conformations, viz. twist (halfchair, symmetry C 2 ) and envelope (symmetry C s ) (Han & Kang, 1996;Riddell et al, 1997). The various possible conformations are described by an imaginary pseudorotation process in which each atom in the ring in turn is displaced out of the plane, becoming the tip of the flap of the envelope.…”