A Triterpene and A Phytosterol from Rhynchosia Minima

The Chemical examination of the n-hexane extract of Rhynchosia minima results the separation of two compounds. To separate these compounds, the dried powder of Rhynchosia minima was succumbed to hot extraction with n-hexane and submitted to chromatography. Mass spectra for the separated compounds appeared their molecular formula which was C30H50O for compound 1 and C29H48O for compound 2. In the 1H-NMR range of compound 1, H-3 proton revealed as a triplet of a double doublet (tdd) at δ 3.13, H-29 protons give two multiplets at δ 4.50 and δ 4.62 and seven methyl protons showed up at δ 27.46, 15.34, 16.09, 15.99, 14.55, 18 and 19.31. In the 1H-NMR range of compound 2, H-3 proton revealed as a triplet of a double doublet (tdd) at δ 3.45, olefinic proton H-6 revealed as a multiplet at δ 5.28 and six methyl protons showed up at δ 12.18, 19.3, 18.97, 21.02, 21.09 and 12.04. From the physical, chemical and spectral characteristics, compound 1 and 2 were distinguished as Lupeol and Stigmasterol.

Divergent Reactivity of 2-Vinylpyridine and 1-Vinylpyrazole in Rhodium-Phosphine Systems: C-H Activation and Dinuclear Chemistry

The Rh^I-Rh^III mixed valence dinuclear complex Rh₂-Cl₂(μ-H)(μ-η²,κ²-C,N-NC₅H₄-2-(Z)CH=CH)(PPhMe₂)₃ has been prepared by reaction of [Rh(μ-Cl)(η²-coe)₂]₂ with 2-vinylpyridine in the presence of dimethylphenylphosphine as a result of C-H activation of the terminal olefinic proton. The X-ray structure presents anagostic Rh···HC and π-π interactions between aromatic rings. In contrast, 1-vinylpyrazole does not undergo a C-H activation process, resulting in the formation of dinuclear species supported by 1-vinylpyrazole bridges. Anagostic Rh···HC interactions and CH···Cl hydrogen bonds are responsible for the 3D packing of the complex.

Cyanoacrylate Inhibitors of the Hill Reaction III. Stereochemical and Electronic Aspects of Inhibitor Binding

Ethoxyethyl 3-octylamino-2-cyanoacrylate and related compounds in which the amino group was replaced by N-CH3, S, O and CH2 were synthesized and their activity as inhibitors of the Hill reaction in isolated pea chloroplasts determined. All compounds showed moderate to high activity but there was no obvious correlation between activity and the electronic character of the ester carbonyl group. The stereochemistry of the various inhibitor molecules was deduced from the PMR spectra and the possible influence of stereochemistry on Hill inhibitory activity discussed. Replacement of the olefinic proton in the 2-cyanoacrylates with a β-alkyl substituent was examined and a specific relationship between the length of the alkyl chain and activity was observed.

Photoreactions of Nitroso Compounds in Solution. XXII. Stereochemical Consequences of the Photoaddition of N-Nitrosopiperidine to Conjugated Acyclic Dienes: a Nuclear Magnetic Resonance Study of Enone Oximes

In the presence of an acid, photoexcited N-nitrosopiperidine adds to conjugated acyclic 1,3-dienes to give the 1,4-adducts as the major product in addition to 1,2-adducts. In the photoaddition to 1,3-pentadienes the reverse 4,1-adduct and 4,3-adducts are also identified. These results suggest that a singlet photoexcited N-nitrosopiperidine–acid complex rapidly decays to piperidinium radical which irreversibly attacks the dienes as the first step, followed by either a short propagation step or a termination step to give C-nitroso compounds. The C-nitroso compounds are rapidly removed by irreversible tautomerization to the final oximes. The reactivity of the piperidinium radical toward conjugated double bonds decreases in the order of RCH=CH2 > cis-RCH=CHR > trans-RCH=CHR. This mechanism is in accord with the following stereochemical results. Firstly, the newly-formed double bond in the 1,4-adduct (or the adduct of the reverse orientation) is exclusively trans-oriented. Secondly, the remaining double bonds in the 1,2-adducts maintain their original stereochemistry.The stereochemistry of the photoadducts, enone oximes 1–11, was determined by means of n.m.r. spectroscopy. From the correlation of the n.m.r. chemical shifts of these enone oximes it has been shown that (i) the α-olefinic proton generally resonates at a lower field than the β-olefinic proton (with one exception) and (ii) in changing from CDCl3 to an aromatic solvent the α-olefinic proton and the α′-alkyl protons are de-shielded by 0.3–0.05 p.p.m. while the β-olefinic proton is shifted only slightly either to a higher or a lower field. It is observed that the order of the chemical shifts of the olefinic protons and the aromatic solvent effects on the chemical shifts in these enone oximes are both opposite to those observed in enone systems.

Solvent effects on the proton spectra of some halopropenes. The preparation and proton resonance spectra of the 1-iodopropenes

The preparation and proton resonance spectra of the 1-iodopropenes are reported and solvent effects on the proton spectra of the chloro-, bromo-, and iodo-compounds are measured. The proton coupling constants are discussed in terms of old and new electronegativity correlations. The olefinic cis and trans proton shifts can be attributed mainly to a paramagnetic contribution from the substituent, whereas the gem olefinic proton shifts depend in addition on the electron-withdrawing power of the substituent. The methyl proton shifts in the 1-substituted compound show little dependence on the substituent and this is discussed in relation to the barrier heights to methyl rotation. The solvent shifts in benzene cannot be completely reconciled with a dipole – induced dipole model. They increase with the size of the substituent and are largest for protons farthest from the substituent. The solvent shifts in acetone can be explained as due to weak hydrogen bonding and reaction field effects. The shifts of protons gem to the substituent arise mainly from hydrogen bonding, whereas the shifts of protons cis or trans have significant contributions from both effects. The reaction field effects can also account for the methyl shifts in acetone.

SOLVENT EFFECTS IN THE NUCLEAR MAGNETIC RESONANCE SPECTRA OF BENZALMALONONITRILES

The nuclear magnetic resonance spectra of a series of substituted benzalmalononitriles were examined in various solvents. The chemical shifts for the olefinic protons are susceptible to large solvent effects which are interpreted as arising from association of a solvent molecule with the olefinic proton (acetone) or a site in its vicinity (benzene). With acetone this leads to a downfield shift from values observed in chloroform. In benzene solution the association produces increased shielding and is present in addition to a second solvation complex, the arrangement of which is governed by the substituent. The difference in behavior of the ethylenic proton in benzalmalononitriles from the formyl proton in benzaldehyde is ascribed to its more highly acidic nature.