High-resolution 500 MHz solution-state 1H and 13C NMR spectra of various poly(lactides) indicate at least hexad stereosequence sensitivity. The poly(lactides) were prepared in vials by melt polymerization of various combinations of l-lactide, d-lactide, and meso-lactide at 180 °C for 3 h using tin(II) bis(2-ethylhexanoate) (tin(II) octoate) as the catalyst in a 1:10 000 ratio. The intensity distribution of the various stereosequence resonances in the NMR spectra indicates a preference for syndiotactic addition during the polymerization process. Minimal evidence of transesterification was observed for these polymerization conditions.

The reactions of acetone and cyclopentanone on a variety of zeolites with different acidities and pore sizes were investigated in detail by both in situ 13C solid-state NMR and ex situ methods following extraction. The overall reaction sequence was acid catalyzed aldol condensations followed by secondary reactions such as double bond migration, hydrogen transfer, and cracking, especially in the more acidic zeolites. The formation of reactive complexes between the ketones and the Bronsted acid sites of the zeolites is implicated as a precursor to condensations at low temperature. The strength of complex formation was reflected in the extent of proton transfer to the ketone, and this was mapped into significant 13C isotropic chemical shift changes. These are interpreted quantitatively as a measure of the effective acidity of the zeolitic environment under actual reaction conditions using a procedure proposed by Farcasiu and coworkers [J. C a r d 1992, 134, 1181. The order of activity for aldol condensations of acetone on the various zeolites (HZSM-5 > HY > HX > NaX, CsX > CsY, CsZSM-5) is in complete agreement with this in situ measurement of acidity. The zeolites studied here were not superacids at 298 K. Free carbenium ions or hydroxycarbenium ions did not form at 298 K as long-lived intermediates from the ketones studied, even at low loadings. The aldol products obtained from acetone and cyclopentanone were generally in agreement with solution chemistry with the exception that shape selectivity was evident in the formation of trindane from cyclopentanone on large pore but not on medium pore zeolites. Cyclohexanone formed products analogous to those of cyclopentanone. The in situ NMR experiments were effective guides to the design of zeolite-based syntheses of aldol products of cyclopentanone using either sealed glass tube or refluxing solvent protocols. The overall results of this investigation suggest the emergence of a physical organic pedagogy that will systematize synthetic reactions using zeolites. Such a methodology would be important in the development of zeolite-based procedures as alternatives to existing routes to fine chemicals that also produce corrosive liquid or metal salt wastes.

A carbon allotrope based on "sp" hybridization containing alternating triple and single bonds (an acetylenic or linear carbon allotrope) has been prepared. Studies of small (8 to 28 carbon atoms) acetylenic carbon model compounds show that such species are quite stable (130 degrees to 140 degrees C) provided that nonreactive terminal groups or end caps (such as tert-butyl or trifluoromethyl) are present to stabilize these molecules against further reactions. In the presence of end capping groups, laser-based synthetic techniques similar to those normally used to generate fullerenes, produce thermally stable acetylenic carbon species capped with trifluoromethyl or nitrile groups with chain lengths in excess of 300 carbon atoms. Under these conditions, only a negligible quantity of fullerenes is produced. Acetylenic carbon compounds are not particularly moisture or oxygen sensitive but are moderately light sensitive.

Solid-state NMR (SSNMR) (1)H T1 and T1ρ relaxation times were used to evaluate the miscibility of amorphous solid dispersions of nifedipine (NIF) and polyvinylpyrrolidone (PVP) prepared by three different methods: melt quenching in the typical lab setting, spray drying and melt quenching in the NMR rotor while spinning. Of the five compositions prepared by melt quenching in the lab setting, the 95:5 and 90:10 NIF:PVP (w:w) amorphous solid dispersions were not miscible while 75:25, 60:40, and 50:50 NIF:PVP dispersions were miscible by the (1)H T1ρ measurements. The domain size of the miscible systems was estimated to be less than 4.5 nm. Amorphous solid dispersions with composition of 90:10 NIF:PVP prepared by spray drying and melt quenching in the NMR rotor showed miscibility by (1)H T1ρ values. Variable-temperature SSNMR (1)H T1ρ relaxation measurements revealed a change in relaxation time at approximately 20 °C below Tg, suggesting increased molecular mobility above that temperature.