The biphenyl-monitored effective size of unsaturated functional or fluorinated ortho substituents.

The size of a series of typical substituents has been probed by dynamic NMR measurements of the barriers to aryl-aryl rotation of the corresponding biphenyls. The resulting B values are meaningful because only mono-ortho substituted compounds were investigated and thus the results are not compromised by the non-additivity of multiple steric effects. On the basis of the chosen model system ethynyl and cyano groups were found to be slightly smaller than a phenyl ring.

The torsional barriers of 2-hydroxy- and 2-fluorobiphenyl: small but measurable.

By making use of a novel diastereotopicity probe, namely C(CF(3))(2)OH, it has been possible to measure by very low temperature (19)F NMR spectroscopy the elusive aryl-aryl rotation barriers of biphenyls bearing an OH or F group in one ortho position. The experimental values (5.4 and 4.

Study of the photobehavior of a newly synthesized chiroptical molecule: (E)-(R(p),R(p))-1,2-bis{4-methyl-[2]paracyclo[2](5,8)quinolinophan-2-yl}ethene.

A new chiroptical compound, (E)-(R(p),R(p))-1,2-bis{4-methyl-[2]paracyclo[2](5,8)quinolinophan-2-yl}ethene (trans-RPQE) has been synthesized, and its photoresponse has been investigated through steady state and time-resolved absorption and emission spectroscopies and theoretical calculations. To elucidate the relaxation mechanism of trans-RPQE after photoexcitation, the photophysics of the 2,4-dimethyl-[2]paracyclo[2](5,8)quinolinophane chromophore has also been studied. The quantum yields of the different relaxation paths for trans-RPQE have been determined.

Electronic and vibrational circular dichroism spectra of chiral 4-X-[2.2]paracyclophanes with X containing fluorine atoms.

The absorption IR and vibrational circular dichroism (VCD) spectra of both enantiomers of 4-X-[2.2]paracyclophanes (X = F, CH(2)F, COCF(3)) have been recorded in the mid-IR and CH stretching regions. The electronic CD (ECD) spectra have been collected as well.

B values as a sensitive measure of steric effects.

Someone who says "A" should be prepared to also say "B": In contrast to cyclohexane model-based A values, biphenyl model-derived B values are powerful tools to quantify steric repulsion in and conformational behavior of ortho-substituted aromatic compounds.Torsional barriers of 15 ortho-substituted biphenyls have been determined computationally using the B3LYP density functional and experimentally by variable-temperature ("dynamic") nuclear magnetic resonance. Taking advantage of the 3'-isopropyldimethylsilyl group as a novel and superior diastereotopicity probe and tracking coalescence temperatures down to -173 degrees C (100 K), activation energies of aryl-aryl rotation as small as 5 kcal mol(-1) can be assessed.

Harmonic and anharmonic features of IR and NIR absorption and VCD spectra of chiral 4-X-[2.2]paracyclophanes.

The vibrational absorption spectra and vibrational circular dichroism (VCD) spectra of both enantiomers of 4-X-[2.2]paracyclophanes (X = COOCD3, Cl, I) have been recorded for a few regions in the range of 900-12000 cm(-1). The analysis of the VCD spectra for the two IR regions, 900-1600 cm(-1) and 2800-3200 cm(-1), is conducted by comparing with DFT calculations of the corresponding spectra; the latter region reveals common motifs of vibrational modes for the three molecules for aliphatic CH stretching fundamentals, whereas in the mid-IR region, one is able to identify specific signatures arising from the substituent groups X.