Markku Mesilaakso

Analysis of the1H and13C{1H} NMR Spectral Parameters of the Tear Gases α-Chloroacetophenone, Dibenz[b,f][1,4]oxazepine, and 2-Chlorobenzylidene Malononitrile

The 1H and 13C{1H} NMR spectra of the tear gases α‐chloroacetophenone, dibenz[b,f][1,4]oxazepine and 2‐chlorobenzylidene malononitrile were recorded in CDCl3, CD2Cl2 and (CD3)2CO and analysed. Assignments of the resonances were confirmed by homonuclear and heteronuclear correlation spectroscopy. Detailed 1H spectral parameters were determined by iterative analysis. The conformations of dibenz[b,f][1,4]oxazepine and 2‐chlorobenzylidene malononitrile were determined on the basis of the long‐range coupling constants 4J(α,ortho), 5J(α,meta) and 6J(α,para). Use of the 1H spectral parameters of dibenz[b,f][1,4]oxazepine for simulation of a reference spectrum is demonstrated for a test sample.

Protonation-deprotonation equilibria in tetrapyrroles Part 2: Mono- and diprotonation of methyl pyropheophorbide a in methanolic hydrochloric acid as verified by the 1H, 13C HSQC and 1H, 15N HMBC NMR experiments

The two-dimensional 1H, 13C and 1H, 15N heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) NMR techniques were applied to investigate the formation of N-protonated cationic species of methyl pyropheophorbide a in methanolic hydrochloric acid (CD3OH-HCl). The 1H, 13C HSQC and 1H, 15N HMBC NMR spectra, recorded at the temperature of 278 K, verified that the CD3OH-HCl solution with [H]+ = 0.021 M, contained the N22-protonated monocations of methyl pyropheophorbide a, whereas the CD3OH-HCl solution with [H]+ = 5.0 M contained the N22, N24-protonated dications of the phorbin. No further protonations to form the trication or tetracation were observed. Consequently, the two middle electronic spectra, which were previously tentatively interpreted as representing the dication and trication, were now attributed to conformational alterations originating from steric hindrance between the central hydrogens and changes in counter-ion and solvation interactions and/or conformational alterations intimately connected to NH-tautomerism. These possibilities to explain the previously observed middle electronic spectra are briefly discussed.

Analysis of 1H and 13C{1H} NMR Spectral Parameters of Diphenylchloroarsine, Diphenylcyanoarsine, and 10-Chloro- 5,10-dihydrophenarsazine: Identification of the Compounds through Reference to Simulated Spectra

The 1H and 13C{1H} nuclear magnetic resonance (NMR) spectra of diphenylchloroarsine, diphenylcyanoarsine, and 10-chloro-5,10-dihydrophenarsazine were recorded from samples prepared in CDCl3, CD2Cl2, and (CD3)2CO. Spectra were analyzed, and detailed 1H NMR spectral parameters were determined by iterative analysis. Simulation of spectra and their use as reference spectra for identification of the compounds under different conditions are discussed.

NMR spectral analysis and molecular dynamics study of 3‐quinuclidinol and 3‐quinuclidinyl benzilate

Proton chemical shifts and coupling constants of 3‐quinuclidinol and 3‐quinuclidinyl benzilate were determined by computer analysis. The relatively broad lines of the quinuclidine protons have their origin in numerous non‐resolved transitions arising from the extensively coupled spin system of 12 nuclei. The signs of the long‐range coupling constants were determined by COSY‐45 and E.COSY. Vicinal coupling constants were converted into proton–proton torsion angles by applying the Altona–Haasnoot equation. Some geometrical ambiguities were revealed, which were studied by molecular dynamics calculations and simulated annealing. The torsion angles and the results from molecular dynamics calculations indicated significant flexibility of the quinuclidine part. For the sake of completeness the carbon chemical shifts of both compounds are presented.

Synthesis and characterization of chlorophyll a enol derivatives: Chlorophyll a tert-butyldimethylsilyl-enol ether and 131-deoxo-131, 132-didehydro-chlorophyll a

Using the sterically hindered base, 1,8-diazabicyclo[5.4.0]undec-7-ene, for enolization and tert-butyldimethylsilyl-trifluoromethanesulfonate for silylation, chlorophyll (Chl) a produced after 15 min at 0 °C in deaerated pyridine solution under argon, after work-up and chromatographic purification on a sucrose column, tert-butyldimethylsilyl-enol ether of Chl a in a yield of 77%. The 131-deoxo-131,132-didehydro-chlorophyll a, was obtained in a yield of 23% through a reaction sequence, where Chl a was first reduced with sodium borohydride to 131(R,S)-hydroxy-Chl a, which via demetalation yielded 131(R,S)-hydroxypheophytin a. In the presence of the sterically hindered base, 1,8-bis(dimethylamino)naphthalene, trifluoroacetylimidazole dehydrated 131(R,S)-hydroxypheophytin a to 131-deoxo-131,132-didehydro-pheophytin a, which after metalation yielded 131-deoxo-131,132-didehydro-Chl a. Using 1,8-bis(dimethylamino)naphthalene and trifluoroacetylimidazole, the straight conversion of 131(R,S)-hydroxy-Chl a to 131-deoxo-131,132-didehydro-Chl a was found unsuccessful. The major products were characterized by electronic absorption spectra (UV-vis) and practically completely assigned 1H and 13C NMR spectra. Some intermediates of the syntheses were also characterized by ESI-TOF mass spectra. Compared with Chl a, the macrocyclic ring-current in the synthesized Chl a enol derivatives was found weakened by the expansion of the π-system to include the isocyclic ring E. Nevertheless, these enol derivatives were still considered to be diamagnetic and aromatic. The possibility of the functional role of the enol derivatives of chlorophyll in photosynthesis is discussed.

Analysis of 1H and 13C{1H} NMR Spectral Parameters and Geometries of Three Isomeric Diphenylbicyclo[2.2.1]Hept-5-Ene-2,3-Dicarboxylic Anhydrides

Abstract Diels-Alder adducts of 1,4-diphenyl-1,3-cyclopentadiene and maleic anhydride were investigated by recording the 1H and 13C{1H} NMR spectra of three isomeric diphenylbicyclo[2.2.1]hept-5-ene endo and exo 2,3-dianhydrides. the spectra were recorded in CD2Cl2 and analysed completely. the effect of the endo and exo configuration of the anhydride ring on the chemical shifts of the bridgehead phenyl protons is discussed. the ortho protons of the exo isomers resonate at higher field than those of the endo isomer, and the resonance pattern of the aromatic protons is narrower in the exo than the endo anhydride. the aromatic regions of the spectra are compared with the same regions of the 1H NMR spectra of the earlier investigated addition products of 1,4-di-p-tolyl-1,3-cyclopentadiene and 1-phenyl-4-p-tolyl-1,3-cyclopentadiene with maleic anhydride. Chemical shifts of the bridge protons are explained on the basis of X-ray data of the compounds and MacroModel calculations on the minimum energy conformations.