Phenyl Hydrogen Atoms Research Articles

Conformational change of L-phenylalanine in fluorinated alcohol-water mixed solvents studied by IR, NMR, and MD simulations

To clarify the unique solvation properties of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) on a biomolecule of L-phenylalanine (Phe), the solvation structure of Phe in HFIP-water mixed solvents at 70 mmol dm−3 has been observed over the entire range of HFIP mole fraction xHFIP using infrared (IR), 1H and 13C NMR techniques with a help of molecular dynamics (MD) simulation. The solvation structure of Phe in the HFIP solvents has been compared with that in 2-propanol (2-PrOH)-water mixed solvents and the structure of L-leucine (Leu) in both alcohol-water mixed solvents previously reported. The results from IR, NMR, and MD simulations showed that water molecules hydrogen-bonded with the Phe carboxylate group are gradually replaced by HFIP with increasing xHFIP. In contrast, the replacement of water molecules by HFIP on the Phe aminium group does not easily take place. These findings arise from the high electron acceptability and the very low electron donicity of the HFIP hydroxyl group due to the electron drawing of the six fluorine atoms. In the 2-PrOH solutions, the replacement of water on the carboxylate group by 2-PrOH less easily occurs with increasing x2-PrOH compared to HFIP because of the lower electron acceptability of 2-PrOH. The solvation for the Phe hydrophilic parts is similar to that of Leu. The most significant difference between HFIP and 2-PrOH was observed for the solvation of the Phe phenyl group. The hydrophobic hydration shell around the phenyl group is collapsed with increasing alcohol content in both alcohol solutions. Instead of water, the HFIP fluorine atoms significantly interact with the phenyl hydrogen atoms, whereas 2-PrOH molecules do not markedly approach the hydrogen atoms. The conformational change of Phe molecule against the dihedral angle of Cγ-Cβ–Cα-COO− takes place with increasing HFIP content, but does not with the increase in 2-PrOH. This is attributed to the steric hindrance between the large phenyl group and the carboxylate group remarkably solvated by HFIP molecules.

Stable 3‐Imino‐2,3‐dihydroindazol‐1‐yl Radicals

AbstractOxidation of 2‐tert‐butyl‐3‐(tert‐butylamino)‐2H‐indazoles with lead(IV) oxide yields red, stable radicals, which can be distilled under high vacuum and recrystallized. They revert to their precursors on Pd‐catalysed hydrogenation. Configuration and atomic distances were obtained by X‐ray diffraction analysis. EPR hfc constants were assigned with the help of 15N labeling and exchange of a phenyl hydrogen atom for a tert‐butyl group. The X‐ray and EPR results show that the novel radicals are to be considered as cyclic hydrazyl radicals, modified by delocalization of the unpaired electron involving the exocyclic imino group and the benzene ring.

New Complexes of Methyldiphenylphosphonium Cyclopentadienylide, Representative of a Class of Ligands Heretofore Much Neglected

Methyldiphenylphosphonium cyclopentadienylide, C5H4PMePh2 (II), has been synthesized and characterized spectroscopically and crystallographically and has been found to exhibit properties consistent with the zwitterionic structure IIb. The new group 6 coordination complexes (η5-C5H4PMePh2)M(CO)3 have been synthesized via substitution reactions of II with M(CO)6 (M = Cr, Mo) or W(CO)3(MeCN)3. Comparisons of ν(CO) values of these complexes with those of the isoelectronic (η6-C6H6)M(CO)3 and [(η5-C5H5)M(CO)3]- suggest that the electron-donating ability of the ylide is less than that of the cyclopentadienyl anion but much greater than that of benzene. Thermal and photochemical substitutions of the CO ligands of (η5-C5H4PMePh2)M(CO)3 (M = Cr, Mo) by equimolar amounts of PMe3 and PPh3 were not observed, but the ylide is displaced photochemically from (η5-C5H4PMePh2)Mo(CO)3 by excess PMe3 to form fac-Mo(CO)3(PMe3)3, while (η5-C5H4PMePh2)Mo(CO)3 reacts with I2 to form [(η5-C5H4PMePh2)Mo(CO)3I]I. The crystal structures of the free ylide and all four of its coordination complexes show that in each case one of the ylide phenyl rings not only eclipses the C5H4 ring but also is oriented toward it in an edge-on fashion. The intramolecular edge−face orientations involve interactions of an aromatic hydrogen atom with the C5H4 aromatic π systems and are rationalized in terms of electrostatic attractive forces between the slightly positive phenyl hydrogen atom and the negatively charged C5H4 ring. The electronic structures of II and of (η5-C5H4PMePh2)Cr(CO)3 have been investigated using ab initio methodologies; it is found that the near-degenerate HOMO and HOMO-1 orbitals of the free ylide exhibit symmetries very similar to those of the corresponding, doubly degenerate HOMO of the cyclopentadienyl anion (E1 symmetry) and that a lower energy, almost fully symmetric orbital corresponds to the fully symmetric bonding A1 MO of the cyclopentadienyl anion. In none of these three orbitals does there appear to be significant π involvement of an orbital on the phosphorus atom, consistent with the low P−C bond order implicit in the zwitterionic structure IIb. The primary ylide−metal interactions in (η5-C5H4PMePh2)Cr(CO)3 involve donation of the HOMO and HOMO-1 orbitals into the dxz and dyz orbitals of the chromium, while the calculated ylide−Cr(CO)3 bond dissociation energy is about 30% higher than the analogous ring−metal bond dissociation energy of (η6-C6H6)Cr(CO)3.

An X-ray Crystallographic and Computational Study of Intermolecular Edge-to-Face Aromatic Interaction in Crystal Structure of exo [4+2]π Cycloadduct of Phencyclone and S-Allyl S-Methyl Dithiocarbonate

Phencyclone reacted with S-allyl S-methyl dithiocarbonate derived from the [3,3]-sigmatropic rearrangement of O-allyl S-methyl dithiocarbonate to give an 1:1 mixture of endo and exo [4+2]π cycloadducts. The single crystal X-ray analysis of the exo [4+2]π cycloadduct was performed. The molecules are linked together with the intermolecular edge-to-face interaction between the phenyl hydrogen atom and the phenanthrene ring. The PM3 calculation reproduced the structural feature of the molecular packing.

Intramolecular hydrogen—deuterium exchange in isomeric methyl ethyl esters of phenylmaleic, -fumaric, and -succinic acids under chemical ionization: low energy CID study and geometrical requirements of the exchange

MH + ions of isomeric methyl ethyl phenylmaleates, 2, and -succinates, 3, obtained by chemical ionization (CI), exhibit preferential collision induced elimination of alcohol involving the 1-alkoxyl group which is adjacent to the phenyl substituent. MD + ions of 2 and 3 exhibit major elimination of ROD under collisional activation, and little (when generated under CD 4-CI) or no (under ND 3-CI) hydrogen—deuterium exchange of the external deuteron with the phenyl hydrogen atoms is observed in this process. The favored collision-induced alcohol elimination from MH + ions of isomeric methyl ethyl phenylfumarates, 4, involves the 4-alkoxyl group. An extensive hydrogen—deuterium exchange and scrambling of the external deuteron with the five phenyl hydrogen atoms precedes the elimination of each of the two alcohols from MD + ions of 4 independent of the reagent gas (CD 4 or ND 3). A practically complete exchange takes place in the course of elimination involving the 4-alkoxyl group. These results are explained in terms of proximity of the 4-alkoxycarbonyl group to the phenyl ring in phenyl fumarates, 4.

Effect of fluorine replacement of hydrogen atoms in aromatic compounds on magnetic shielding of nuclei of heavy atoms at a distance from position of substitution

From13C,15N,17O,19F,29Si,31P,73Ge,77Se,119Sn, and125Te NMR data, it follows that complete replacement of phenyl hydrogen atoms by fluorine in compounds C6H5X leads to a systematic increase in shielding of nuclei in the ring carbon atom bonded to the X group and in shielding of the nucleus of the α-atom of X, along with deshielding of the nuclei of the Β- and γ-atoms of X. The effect evidently has a long-range character and can be described by the extended theory of Dewar and Kelemen.

Synthesis and some reactions of a terminal carbyne complex of osmium. Crystal structures of Os(CR)Cl(CO)(PPh 3) 2 and [formula omitted]gCl]R)Cl(CO)(PPh 3) 2

The reaction of two equivalents of LiR (R = p-tolyl) with the dichlorocarbene complex OsCl 2(CCl 2)(CO)(PPh 3) 2 gives the carbyne complex Os(CR)Cl(CO) (PPh 3) 2 (I) in good yield. X-ray crystal structure determination shows that I is mononuclear with an OsC distance of 1.78(2) Å. The OsC bond reacts with electrophiles rather than nucleophiles. Thus, HCl adds to give the alkylidene complex OsCl 2(CHR)(CO)(PPh 3) 2, Cl 2 forms OsCl 2(CClR)(CO)(PPh 3) 2 and sulphur, selenium and tellurium react to yield to corresponding dihapto-chalcoacyls Os(η 2-C[X]R)Cl(CO)(PPh 3) 2 (X = S, Se, Te). Group Ib metal halides also add to the OsC bond to form the adducts Os(C[M X]R)Cl(CO)(PPh 3) 2 (MX = CuI, AgCl, AuCl). The X-ray crystal structure determination of Os(C[A gCl]R)Cl(CO)(PPh 3) 2 (II) suggests that this complex can be considered as a dimetallacyclopropene derivative. Crystals of I are monoclinic, space group P2 1/ n, a 17.030(2), b 12.774(1), c 18.315(3) Å, β 107.96 (1)°, V 3793.2 Å 3, Z = 4, D m 1.53(1), D c 1.54. Crystals of II are monoclinic, space group P2 1/ n, a 13.021(2), b 23.714(2), c 12.999(2) Å, β 90.556(2)°, V 4013.7 Å 3, Z = 4, D m 1.705(5), D c 1.695. The structures were solved by conventional heavy-atom methods, and refined by full-matrix least-squares employing anisotropic thermal parameters for all non-hydrogen atoms except for the carbon atoms of the phenyl rings. Phenyl hydrogen atoms were included in calculated positions. Final residuals R were 0.040 and 0.037, respectively.

The crystal structure of diiodo(( o-methylthiophenyl)diphenylphosphine)palladium(II), a complex exhibiting a large structural trans influence

The crystal structure of the title compound has been determined by conventional X-ray diffraction techniques. The red diamond-shaped crystals are monoclinic, space group P2 1/ n, a 8.914(4), b 16.090(12), c 14.991(5) Å, β 95.97(2)°, V 2138.44 Å 3, Z = 4. Refinement by full-matrix least-squares methods employed anisotropic thermal parameters for all non-hydrogen atoms and isotropic temperature factors for hydrogen atoms, and returned final residuals of R = 0.028 and R w = 0.028. The complex is monomeric, with a square planar coordination geometry comprising the S and P atoms of the bidentate ( o-methylthiophenyl)diphenylphosphine ligand and the two iodine atoms. The PdI distance trans to P is 2.658(1) Å whereas that trans to S is 2.602(1) Å. The difference of 56 standard deviations illustrates the greater structural trans influence of phosphine over thioether donors. The PdP and PdS distances of 2.250(2) and 2.288(2) Å, respectively, are normal. Two phenyl hydrogen atoms approach the Pd atom in the axial regions above and below the square plane at distances of 2.98 and 2.99 Å.

The molecular and crystal structure of p‐methyl‐phenyl glyoxylacid‐m‐trifluoro‐anilide

AbstractUsing X‐ray crystal structure analysis of the title compound the positions of all atoms (including all A atoms) were localized in the triclinic unit cell with the parameters a = 14.686 Å, b = 7.700 Å, c = 7.898 Å, α = 122.5°, β = 105.4°, γ = 87.7°, space group P1. The existence of an intramolecular HN … O(1) bridge was inferred, the H‐bridge acceptor of which predominantly is the π‐electron density of the carbonyl group in agreement with the results of the X‐ray crystal structure analysis of p‐methyl‐phenyl‐glyoxyl‐acid‐p‐chloroanilide (HOEHNE, SEIDEL). Moreover, the existence of H‐bridgelike interactions of the two phenyl hydrogen atoms H(6) and H(15) to the carbonyl oxygen O(2) could be proved. These interactions stabilize the conformation of the two phenyl rings in the molecule.

The Molecular and Crystal Structure of p‐methyl‐phenyl‐glyoxyacid‐p‐chloranilide

AbstractUsing X‐ray crystal structure analysis of the title compound the positions of all the atoms (including all H atoms) in the monoclinic unit cell with the parameters a = 13.900 Å, b = 5.138 Å, c = 17.956 Å and β = 91.05° and the space group P 21/n were localized. The existence of an intramolecular N—H(N)…︁ O(1)‐bridge was inferred, whose H‐bridge acceptor predominantly is the π‐electron density of the carbonyl group. At the same time the H(N) atom participates in the intermolecular bridge NH(N)…︁ O′(1) to the symmetry‐equivalent neighbouring molecule. H‐bridge‐like interactions of the two phenyl hydrogen atoms H(6) and H(15) to the carbonyl oxygen O(2) have also been inferred from the torsion angles.

The structure of hexafluoroacetone azine bis(triphenylphosphine)platinum

The crystal structure of hexafluoroacetone azine bis(triphenylphosphine)platinum, C 42H 30F 12N 2P 2Pt, has been determined by single-crystal X-ray diffraction techniques. The compound crystallizes in the monoclinic space group C2/ c with a 31.155(3), b 13.091(1), c 21.828(2) Å, β 109.23(1)° and Z = 8. Manual diffractometer methods (Cu radiation, λ 1.54050 Å) were used to obtain 5046 reflections with I net ⩾ 8 counts sec −1 at 21°C. The structure was solved by the heavy atom method and was refined, including CH 2Cl 2 at occupancy 0.4 on a crystallographic 2-fold axis, by block-diagonal least-squares methods to R = 0.056. Location of the phenyl hydrogen atoms was not attempted. The platinum atom is σ-bonded to one CN of the azine ligand forming a PtCN three-membered ring. Coordination about platinum consists of a slightly distorted square-planar arrangement of the phosphorus atoms and the bonded carbon and nitrogen atoms of the unsaturated ligand. The observed difference in PtP bond lengths is rationalized in terms of the trans-influence.

Crystal structure of 5,5-dimethyl-2-p-bromophenylimino-?3-1,3,4-oxadiazoline

Oxidation of acetone-4-p-bromophenylsemicarbazone with lead tetraacetate yields only one isomer of 5,5-dimethyl-2-p-bromophenylimino-Δ3-1,3,4-oxadiazoline, C10H10BrN3O. Crystals of this compound are triclinic, space groupP¯1,a = 5·91(1),b = 9·52(1),c = 11·59(2) A, α =114·1(1) °, β = 93·5(1) ° and γ = 108·8(1) °;z = 2 and the chemical composition is C10H10BrN3O. Of 2306 independent reflexions examined, 877 were strong enough to be measured with integrated precession photographs using MoKα radiation. The structure was refined using a full-matrix least-squares program to a finalR value of 0·064. The structure consists of planar phenyl and oxadiazoline rings, with a van der Waals interaction between a phenyl hydrogen atom and oxygen atom of the five member ring preventing the two rings from being co-planar; the H(13)-O(1) separation is 2·47 A. TheZ-configuration of the product suggests a specific mechanism for the ring closure involving an organolead intermediate.