Hitoshi Senda

A comparative vibrational and NMR study of cis-cinnamic acid polymorphs and trans-cinnamic acid.

The IR and Raman spectra of the two polymorphic forms (58 degree- and 68 degree-forms) of cis-cinnamic acid were measured, and the spectral differences discussed on the basis of the crystal structures of the two forms. The IR bands related to the COOH group differ in the frequencies and band shape, reflecting differences in the hydrogen bonding between the two modifications. These spectra were compared with those of trans-cinnamic acid. The IR, Raman, and NMR spectra of the isotopic compounds, including the deuterated and 13C analogs of the cis and trans acids, were also recorded in the solid state and in solution to confirm the spectral assignments.

Molecular structure and vibrational spectra of phenolphthalein and its dianion

Infrared (IR) and Raman spectra of phenolphthalein (PP) and its dianion form (sodium and potassium salts) were studied both in the solid state and in aqueous solution. Band assignments were carried out on the basis of the isotope shifts of the ring deuterated and 13C-substituted derivatives. Spectral analyses reveal that the PP dianion exists as mixtures of the benzenoid form (colorless) and the quinonoid form (colored) in the solid state and in aqueous solution, while the neutral PP solely takes the gamma-lactone form. This work provides the first vibrational spectroscopic evidence for the coexistence of the two species in the PP dianions.

Chemoselective isomerization of amide-substituted oxetanes with Lewis acid to give oxazine derivatives or bicyclic amide acetals

The Lewis-acid catalyzed isomerization of secondary and tertiary amide-substituted oxetanes takes place chemoselectively, giving 5-hydroxymethyl-5,6-dihydro-4H-1,3-oxazines and reactive amide acetals consisting of a bicyclo[2.2.2]octane skeleton, respectively.

Substituent Effect on the Cationic Monomer-Isomerization Polymerization of (Cyclic Imide)-Substituted Oxetanes with Two Different Ring-Opening Routes

This study reports the effect of substituent on the cationic monomer-isomerization ring-opening polymerization of 3-(R 1 -methyl)-substituted 3-R 2 -oxetanes (1), in which R 1 is phthalimide, maleimide, succinimide, or glutarimide and R 2 is ethyl, benzyl, phenyl, or isopropyl. The acid-catalyzed polymerization of 1 gave polyacetal (3) or polyether (4), together with an isomeric bicyclic acetal (2). The isomerization of 1 to 2 took place prior to polymerization. Subsequently the polymerization of 2 occured by either single or double ring opening depending on temperature. The polymerization mechanism is discussed in detail based on the coordination of 1 to Lewis acid and the substituent effect on the polymerization manner. In the double ring-opening polymerization of 2 at 130°c, a carbon-carbon double bond of the lactam ring was indispensable for stabilizing the carboxonium-propagating end. Therefore, 2 carrying a saturated lactam ring did not polymerize in such a manner. Phenyl-substitued oxetane phthalimide was unique in undergoing an unusual cyclodimerization at 130°C, primarily because of the high susceptibility of the neophyl-type carbon skeleton to a cation transfer. On the other hand, most 2 brought about the single ring-opening polymerization below room temperature, regardless of the lactam substituent and the R 2 group. This polymerization was an equilibrium polymerization through a bicyclic oxonium-propragating end, and the thermodynamic parameters of polymerization were determined. Thus, 3 was transformed into 4 in one pot, by a combination of the depolymerization of 3 and the repolymerization of 2 above the ceiling temperature. From the structure analysis of 2 it was inferred that the single ring-opening polymerizability arises from dipole-dipole repulsion between the parallel standing lone pairs of two acetalic oxygen atoms in a nearly symmetric bicycle. There fore, 2 having a somewhat twisted bicyle showed no single ring-opening polymerizability.

Polymorphism of phenylpyruvic acid studied by IR, Raman and solid state 13C NMR spectroscopy

Abstract Polymorphs I and II of phenylpyruvic acid are obtained as mixtures of both crystal forms or relatively pure crystals, from different solvents. Polymorph I is more stable than polymorph II at room temperature. Spectral characteristics of these polymorphs are discussed on the basis of IR, Raman and solid state 13 C NMR spectra. Also, the assignment of the IR features observed in the 1600–1700 cm −1 region is re-investigated by referring to the spectra of heavy-atom substituted derivatives. It is suggested that the CO stretching band is split by the crystal field for both polymorphs.

Molecular Structure and Dimerization of d-Cycloserine in the Solid State

Abstract d-cycloserine (CS) is transformed into cis-3, 6-bis(aminooxymethyl)-2, 5-piperazinedione (CS-dimer) in the solid state under a humid atmosphere. This dimerization process was followed by measuring the IR bands characteristic of CS and CS-dimer. The reaction was accelerated by the presence of increased water vapor. The X-ray analysis of CS monohydrate (CS · H2O) revealed that the CS molecules exist as a zwitter ion where the α-amino N atom is protonated and the amide N atom is deprotonated in the crystal. Participation of water molecules was suggested in the dimerization of CS.

IR Study on Aqueous Solution Behavior of D-Cycloserine

Abstract IR spectra were measured for an antitubercular agent, D-cycloserine (CS), and the hydrolyzate, β-aminooxy-D-alanine (AOA) and the dimer, cis-3, 6-bis(aminooxymethyl)-2, 5-piperadinedione (CS-dimer) at various pHs in aqueous solutions. Molecular species existing in the ionic equilibria were characterized by the pH dependence of the spectra. Band assignments were carried out by reference to the spectra of D20 solutions and those of related compounds. Spontaneous transformation of CS to CS-dimer was observed by the IR spectra for the neutral aqueous solution. The spectral evidence suggested that the non-ionic form of CS plays a key role in the dimerization process.

Keto-Enol Tautomerism of Mono-Substituted Phenylpyruvic Acids as Studied by NMR and PM3 Calculation

Abstract Keto-enol tautomerism of mono-substituted phenylpyruvic acids has been studied by the 1H and 13C NMR spectra. The equilibrium constants and the kinetic parameters for the tautomerism were obtained from the spectral data. The equilibrium constants are strongly dependent on the position of the substitution; the values for the o-substituted PPAs are several times greater than those of the m- or p-substituted derivatives. The PM3 calculations have been carried out to obtain the information on the preferred conformations of the tautomers and on the mechanism for the tautomerism. The results suggest the involvement of a solvent molecule in the equilibrium process.

Ring-chain tautomerism of halogenated phenolphthaleins: Vibrational spectroscopic and semiempirical MO study

Ring-chain tautomerism of halogenated phenolphthaleins and the effect of the halogen substitution have been studied by vibrational spectroscopic and semiempirical MO methods. The vibrational spectra indicate that the content of the colored species (carboxylate form) increases on the substitution of the isobenzofuranone ring, whereas the colorless species (lactone form) becomes dominant on the substitution of phenolic rings. MO calculations have revealed that the substitution of either ring does not change the basic property of the electronic transition of the colored species and that the relative stability of both forms is dependent on the substitution type in accord with the results of the vibrational study.

Molecular structure of methyl phenylpyruvates studied by 1H NMR and IR spectroscopies and quantum mechanical calculations

Abstract Molecular structure of methyl phenylpyruvate (MPP) and its p -substituted derivatives has been investigated by 1 H NMR and IR spectroscopies. The spectral data point out that MPPs take the enol form both in solution and in the solid state. The ab initio calculations were carried out in order to get information on the configurational and conformational preferences in the enol form. It is suggested from the calculation that the inter- and intra-molecular hydrogen bondings between the enol OH group and the ester C  O group are important for stabilization of the conformer.