RESUMO
Our study on the exact timing and the potential climatic, environmental, and evolutionary consequences of the Laschamps Geomagnetic Excursion has generated the hypothesis that geomagnetism represents an unrecognized driver in environmental and evolutionary change. It is important for this hypothesis to be tested with new data, and encouragingly, none of the studies presented by Picin et al. undermine our model.
RESUMO
Our paper about the impacts of the Laschamps Geomagnetic Excursion 42,000 years ago has provoked considerable scientific and public interest, particularly in the so-called Adams Event associated with the initial transition of the magnetic poles. Although we welcome the opportunity to discuss our new ideas, Hawks' assertions of misrepresentation are especially disappointing given his limited examination of the material.
RESUMO
We report quantum yields following 266 nm photolysis of trans-2,3-diphenyloxirane (TDPO) for the formation of the trans-ylide (Scheme 1, Phi = 0.099 +/- 0.014), cis-2,3-diphenyloxirane (CDPO, Phi = 0.10 +/- 0.009), benzaldehyde (Phi = 0.47 +/- 0.04), and deoxybenzoin (Phi = 0.077 +/- 0.002). Photolysis of TDPO may lead to both orbital symmetry allowed and forbidden products, but the trans-ylide decays solely via an orbital symmetry predicted pathway to CDPO. Coupling our quantum yields to results of Das and co-workers,(1) we report an extinction coefficient for the trans-ylide of 9.4 x 10(4) M(-)(1) cm(-)(1) at 470 nm. We also report pseudo-first-order rate constants for the reaction between maleic anhydride and the trans-ylide in acetonitrile (k(Q) = 3.32 +/- 0.04 x 10(9) M(-)(1) s(-)(1)) and in cyclohexane (k(Q) = 5.36 +/- 0.07 x 10(9) M(-)(1) s(-)(1)) and between fumaronitrile and the trans-ylide in acetonitrile (k(Q) = 1.57 +/- 0.02 x 10(9) M(-)(1) s(-)(1)) and cyclohexane (k(Q) = 3.69 +/- 0.04 x 10(9) M(-)(1) s(-)(1)). We report the crystal structure of rac-(2R,3R,4R,5R)-3,4-dicyano-2,5-diphenyltetrahydrofuran, the sole product of 1,3-dipolarophilic addition between the trans-ylide and fumaronitrile in cyclohexane. A brief discussion of solvent and steric effects in 1,3-dipolarophilic additions is included.