The crystal and molecular structure of 4-methyl-2-phenyl-(3<i>H</i>)-1,3,5,2-oxadiazaboroline

Raper, Eric S.

doi:10.1107/s0567740878010651

Cited by 8 publications

(4 citation statements)

References 5 publications

(3 reference statements)

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“…Ten have been made with ring substituents: 19 , 42 , 46 , 53 , 56 , 59 , 63 , 76 , 85 , 87 , and two others with a fused ring: 22 16 and 26 . Experimental X-ray structures are available for five of the 12, 19 , , 42 , 46 , ,, 56 , and 76 , , but there is gas-phase electron diffraction data in only one case, 56 ,− Infrared, and occasionally Raman, data have been reported for 19 , , 22 , − 26 , 46 , , 53 , 59 , 63 , and 76 . ,, Dipole moments have been measured only for variants of 19 .…”

Section: Introductionmentioning

confidence: 99%

Structures, Vibrational Frequencies and Polarizabilities of Diazaborinines, Triazadiborinines, Azaboroles, and Oxazaboroles

Doerksen

Thakkar

1999

J. Phys. Chem. A

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Ab initio, second-order, Møller−Plesset perturbation theory calculations of the equilibrium geometries, harmonic vibrational frequencies, relative stabilities, dipole moments, and static dipole polarizabilities are reported for 70 different 6π-electron monocycles containing boron and nitrogen. These include 26 azaborinines isosteric to pyridine, 16 azaboroles, and 28 oxazaboroles. The most stable isomers have the substructure XBHNH, where X = N, NH, or O is the base-ring heteroatom. Planar conformations are stable minima for all but 15 five-membered rings. Lower level calculations are unreliable in predicting which molecules are planar. Good agreement is found with the available electron diffraction and X-ray structures of substituted rings. Additive atom and bond polarizability models which are accurate to within a few percent are constructed for a larger set of 104 planar molecules, including azines, azoles, oxazoles, and azaborinines isosteric to benzene. The presence of boron causes scatter of the polarizabilities of isomers; hence the additive models of polarizability are less accurate than if only heterocycles containing C, N, and O are included.

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Section: Introductionmentioning

confidence: 99%

Structures, Vibrational Frequencies and Polarizabilities of Diazaborinines, Triazadiborinines, Azaboroles, and Oxazaboroles

Doerksen

Thakkar

1999

J. Phys. Chem. A

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“…Mit Phenylboronsäure war aus einem aliphati schen Amidoxim bereits ein Borol-Derivat darge stellt [4] und auch eine Röntgenstrukturanalyse beschrieben worden. Deshalb setzten wir 2 noch exemplarisch mit Phenylboronsäure um und er hielten auch hier die Verbindung 10.…”

unclassified

“…14, mit den diffraktometrisch (Syntex P 2,, G raphitm onochrom ator, M oK a, X = 0,71073 Ä) aus 15 Reflexen (33,9 < 2 6 < 36,0°) ermittelten G itterkonstanten a = 5,574 (2) Die A tom zuordnung im heterozyklischen Ring basiert sowohl auf der Lokalisierung des H-Atoms am Atom N 4 als auch auf geometrischen und bin dungstheoretischen Überlegungen [7]. Die Z uord nung ist auch im Einklang mit der Struktur eines vergleichbaren Borols, 4-Methyl-2-phenyl-2,3-dihydro-l,3,5,2-oxadiazaborol [4], bei dem der Phe nylring zwischen Heterozyklus und Methylgruppe entfallen ist. Abgesehen von der Einfachbindung -4-( 4-methylphenyl) -2,3-dihydro-1,3 -4-( 2-methylphenyl) -2,3-dihydro-1,3,5,2-oxadiazaborol (1 0 ) 1 mmol 2 und 1 mmol Phenylboronsäure wer den mit 40 ml Benzol 5 h am W asserabscheider er hitzt.…”

unclassified

Cyclisierung von Amidoximen mit Oxybis(diphenylboran) / Cyclization of Amidoximes with Oxybis(diphenylborane)

Möhrle¹,

Bluhme-Hensen²,

Middelhauve

et al. 1991

Zeitschrift Für Naturforschung B

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“…Crystallographic data is available for a large number of "organic boronic acids" [R-B(OH) 2 ] and "peptide boronic acids" [AA-CONH-C(R)H-B(OH 2 )], but no experimental data are yet available for boronamides. However, the crystal structure 28 of a cyclic boron derivative, 4-methyl-2-phenyl-(3H)-1,3,5,2-oxadiazaboroline (Chart 1), which is related to NMB has been reported. The B-O bond length in NMB is found to be 1.391-1.395 Å (Table 2) at the MP2(full)/6-31+G* level of theory.…”

Section: Resultsmentioning

confidence: 99%

The B(OH)−NH Analog Is a Surrogate for the Amide Bond (CO−NH) in Peptides: An ab Initio Study

Malde

Khedkar

Coutinho

2006

J. Chem. Theory Comput.

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The conformational preferences of N-methyl-methylboronamide (NMB), a B(OH)-NH analog of the amide CO-NH in natural peptides, have been investigated at the Hartree-Fock; Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Parr; and second-order Møller-Plesset levels of theory with the 6-31+G* basis set. The minima, saddle points, and rotation barriers on the potential energy surface of NMB have been located and the energy barriers estimated. Besides the global minimum, there are three local minima within 2.0 kcal mol(-)(1) of the global minimum characterized by specific ω and τ torsion values. The energy barriers for rotation about the "ω angle" are 16.4-18.8 kcal mol(-)(1) and are a consequence of the double-bond character of the B-N bond as revealed by natural bond orbitals calculations. The "ω angle" and the ω rotation barrier are nearly the same as those seen in natural peptides. The τ rotation barriers (B-O bond) are relatively low because of the single-bond character of the B-O bond. Ala-BON, the Ala-dipeptide derived from NMB, has been constructed as a model peptide to study the conformational preferences about the φ and ψ torsion angles. The study reveals a strong preference for α-helix, type-II β-turn, 2.27 ribbon, and antiparallel β-sheet conformations, and mirror images of both type-II β-turn and 2.27 ribbon motifs whose φ and ψ values fall in the "disfavored regions" of the Ramachandran map. Thus, the replacement of the carbonyl group by B-OH retains the geometry and barrier around the "ω angle" and induces a strong preference for regular secondary structure motifs and also structures with positive φ values. This makes the B(OH)-NH analog an important surrogate for the peptide bond, with the additional advantage of stability to proteolytic enzymes.

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The crystal and molecular structure of 4-methyl-2-phenyl-(3H)-1,3,5,2-oxadiazaboroline

Cited by 8 publications

References 5 publications

Structures, Vibrational Frequencies and Polarizabilities of Diazaborinines, Triazadiborinines, Azaboroles, and Oxazaboroles

Structures, Vibrational Frequencies and Polarizabilities of Diazaborinines, Triazadiborinines, Azaboroles, and Oxazaboroles

Cyclisierung von Amidoximen mit Oxybis(diphenylboran) / Cyclization of Amidoximes with Oxybis(diphenylborane)

The B(OH)−NH Analog Is a Surrogate for the Amide Bond (CO−NH) in Peptides: An ab Initio Study

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