Apical splitting

Due to the relative lability of the apical Sn—R bond in carbastannatranes 441, these compounds are interesting synthons for further chemical transformations636,873. For example, under ultrasonic induction even methanol is capable of splitting the Me—Sn bond in carbastannatrane 441a819. 

Optically active metal complexes have been recognized as excellent catalysts for the enantioselective cyclopropanation of carbenes with alkenes. Normally, diazo compounds react under metal catalysts in the dark to afford carbenoid complexes as key intermediates. Katsuki et al. have reported the ds-selective and enantioselective cyclopropanation of styrene with a-diazoacetate in the presence of optically active (R,R)-(NO + )(salen)ruthenium complex 80, supported under illumination (440 nm light or an incandescent bulb) [59]. The irradiation causes dissociation of the apical ligand ON + in 80, and thus avoids the splitting of nitrogen from the a-diazoacetate. 

However, the detailed studies of NMR spectra led to the conclusion about the interchange of apical and equatorial fluorine atoms. Since the apical and equatorial bonds P—F in PF5 have different lengths, the NMR spectrum can be expected to consist of two doublets with integral intensity ratio 2 3. Actually, the observed NMR spectrum of PF5 (at F) has one doublet caused by spin-spin interaction of P and F nuclei, i.e. the splitting of signals from axial and equatorial fluorine atoms is absent. 

In Reference 3, two distinct ESR spectra were identified for potassium clusters in argon matrices. Both spectra have doublet ground states (S = h) and a well resolved hyperfine (hf) structure arising from the Fermi contact interaction of the unpaired electron spin with three I = h nuclei. Seven groups of four transitions each were assigned to a potassium trimer of 62 symmetry whose apical and two equivalent terminal atoms have hf splitting... 

F nuclear magnetic resonance data there are two fluorine environments, a low-field doublet and a high-field triplet, each component being further split into a septuplet because of coupling between F and the methyl protons. The doublet is due to apical F atoms /p.f = 772 c.p.s. 5 = — 74p.p.m. (from an external trifluoroacetic acid reference). (Checkers find 776 and —74.3, respectively.) The high-field triplet is due to the equatorial F atoms Jp.f = 960 c.p.s. 5 = 4-9.8 p.p.m. (from an external trifluoroacetic acid reference). (The checkers find 960 and 4-9.8, respectively.)... 

Dehiscence is called porous or apical when the seeds escape through pores at the apex, as in the Poppy valvular, when valye-like orifices form in the wall of the capsule.. Valvular dehiscence is septicidal, when the constituent carpels of a pericarp become disjoined, and then open along their ventral suture. Example Colchicum loculi-cidal, dehiscence into loculij or cells, in wWch each component carpel splits down its dorsal suture, and the dissepiments remain intact. Example Cardamon septifragal dehiscence, a breaking away of the valves from the septa or partitions. Example Orchids (Fig. 98). 

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