Intramolecular Hypervalent Interaction in the Conjugate Five-Membered Rings

Role of alkyl silatranes as plant growth regulators: comparative substitution effect on root and shoot development of wheat and maize

BACKGROUND

The present investigation reports the stimulating effects of different substituted alkyl silatranes (3a-3e) on the early seedling growth of wheat (Triticum aestivum) and maize (Zea mays). Seeds of these plants were exposed to six different concentrations (0, 10, 50, 100, 200 and 500 µmol L^-1 ). The results revealed that different substitutions (3a-3e) had different effects on root and shoot elongation. Silatranes (3a-3e) were synthesized employing microwave irradiation by a solvent-mediated transesterification reaction, thereby reducing reaction times from several hours under conventional reflux conditions to 15 min under microwave irradiation.

RESULTS

It was of interest that the effect of these silatranes did not show a dose-dependent relationship but an optimum concentration, which was 100 µmol L^-1 for maize and 200 µmol L^-1 for wheat. γ-Aminopropyl silatranes (3b and 3e) gave the best results in maize, whereas γ-chloropropyl silatrane (3a) was most efficient for wheat at these optimum concentrations.

CONCLUSION

All the synthesized silatranes were effective in promoting root and shoot growth of wheat and maize. Furthermore, an efficient green microwave methodology was successful for the synthesis of silatranes. These observations pave the way for silatranes as efficient plant growth regulators for crops. © 2018 Society of Chemical Industry.

Computational evidence that hyperconjugative orbital interactions are responsible for the stability of intramolecular Te⋯O/Te⋯S non-covalent interactions and comparable to hydrogen bonds in quasi-cyclic systems

The intramolecular secondary bonding interactions involving quasi-cyclic tellurium are comparable to H-bond strength and partially governed by orbital interactions.

An unusually stable chlorophosphite: What makes BIFOP-Cl so robust against hydrolysis?

Two chlorophosphites, the biphenyl-based BIFOP-Cl and the diphenyl ether-based O-BIFOP-Cl, exhibit striking differences regarding their reaction with water. While BIFOP-Cl is nearly completely unreactive, its oxo-derivative O-BIFOP-Cl reacts instantly with water, yielding a tricyclic hydrocarbon unit after rearrangement. The analysis of the crystal structure of O-BIFOP-Cl and BIFOP-Cl revealed that the large steric demand of encapsulating fenchane units renders the phosphorus atom nearly inaccessible by nucleophilic reagents, but only for BIFOP-Cl. In addition to the steric effect, a hypervalent P(III)-O interaction as well as an electronic conjugation effect causes the high reactivity of O-BIFOP-Cl. A DFT study of the hydrolysis in BIFOP-Cl verifies a higher repulsive interaction to water and a decreased leaving tendency of the chloride nucleofuge, which is caused by the fenchane units. This high stability of BIFOP-Cl against nucleophiles supports its application as a chiral ligand, for example, in Pd catalysts.

Structural Conformers of (1,3-Dithiol-2-ylidene)ethanethioamides: The Balance between Thioamide Rotation and Preservation of Classical Sulfur-Sulfur Hypervalent Bonds

The reaction of N-(2-phthalimidoethyl)-N-alkylisopropylamines and S2Cl2 gave 4-N-(2-phthalimidoethyl)-N-alkylamino-5-chloro-1,2-dithiol-3-thiones that quantitatively cycloadded to dimethyl or diethyl acetylenedicarboxylate to give stable thioacid chlorides, which in turn reacted with one equivalent of aniline or a thiole to give thioanilides or a dithioester. Several compounds of this series showed atropisomers that were studied by a combination of dynamic NMR, simulation of the signals, conformational analysis by DFT methods, and single crystal X-ray diffraction, showing a good correlation between the theoretical calculations, the experimental values of energies, and the preferred conformations in the solid state. The steric hindering of the crowded substitution at the central amine group was found to be the reason for the presence of permanent atropisomers in this series of compounds and the cause of a unique disposition of the thioxo group at close-to-right angles with respect to the plane defined by the 1,3-dithiole ring in the dithiafulvene derivatives, thus breaking the sulfur-sulfur hypervalent bond that is always found in this kind of compounds.