A nuclear magnetic resonance study of tert-butylaldehyde and tert-butyliodide

Deuterium nuclear magnetic resonance lineshapes for polycrystalline (CD 3 ) 3 CCHO and (CD 3 ) 3 CI have been investigated between 100 K and the melting point of each sample. As in other tert-butyl compounds, rotational motion of methyl and tert-butyl groups occurs in the lowest temperature phase, while the solid phase just below the melting point is characterized by overall molecular rotations in both tert-butylaldehyde and tert-butyliodide. The "rotator" phase is observed in tert-butyliodide-d 9 between 239 and 212 K only upon cooling; no solid–solid phase transition is observed upon heating. In (CD 3 ) 3 CCHO, two solid–solid phase transitions are observed at 165 ± 5 K and 190 ± 2 K. Deuterium nuclear magnetic resonance lineshapes in the solid II phase are consistent with rapid 180° flips about a pseudo-C 2 axis. Deuterium spin-lattice relaxation times were measured in the liquid, solid I, and solid II phases of (CD 3 ) 3 CCHO, and in the liquid and rotator phases of (CD 3 ) 3 CI and (CD 3 ) 3 CCl. The data for both the chloride and the iodide compounds indicate a discontinuous increase in the rotational correlation time upon melting, similar to that observed in (CD 3 ) 3 CBr and (CD 3 ) 3 CSH. However, neither 2 H nor 13 C T 1 's of the methyls indicate that a discontinuity occurs at the melting point for tert-butylaldehyde. Carbon-13 and 17 O relaxation times of the aldehyde substituent support this result.