Aminophosphanes with bulky amino groups: Molecular structure,coupling constants 1J(31P, 15N) and 2J(31P, 29Si), and isotope‐induced chemical shifts 1Δ14/15N(31P)

The preferred conformation of aminophosphanes with bulky amino groups ( 1–20 ) was determined by NMR spectroscopy in solution, in two cases in the solid state ( 11,17 ) and in one case ( 11 ) by X‐ray crystallography. Trimethylsilylaminodiphenylphosphanes Ph₂PN(R)SiMe₃ (R = Bu ( 1 ), Ph ( 2 ), 2‐pyridyl ( 3 ), 2‐pyrimidyl ( 4 ), Me₃Si ( 5 )), amino(chloro)phenylphosphanes Ph(Cl)PNRR′ (R = Bz, R′ = Me ( 6 ), R = Bz, R′ = ^tBu ( 7 ), R = Et, R′ = Ph ( 8 )), amino(chloro)tert‐butylphosphanes ^tBu(Cl)PNRR′ (R = R′ = ⁱPr ( 9 ), R = Me, R′ = ^tBu ( 10 ), R = Bz, R′ = ^tBu ( 11 ), R = H, R′ = ^tBu ( 12 ), R = Et, R′ = Ph ( 13 ), R = ⁱPr, R′ = Ph ( 14 ), R = Bu, R′ = Ph ( 15 ), R = Bz, R′ = Ph ( 16 ), R = R′ = Ph ( 17 ), R = R′ = Me₃Si ( 18 )), 3‐tert‐butyl‐2‐chloro‐1,3,2‐oxazaphospholane ( 19 ), and benzyl(tert‐butyl)aminodichlorophosphane ( 20 ) were studied by ¹H, ¹³C, ¹⁵N, ²⁹Si, and ³¹P NMR spectroscopy. In all cases, the more bulky substituent at the nitrogen atom prefers the syn‐position with respect to the assumed orientation of the phosphorus lone pair of electrons. Many of the derivatives studied adopt this preferred conformation even at room temperature. Numerous signs of coupling constants ¹J(³¹P, ¹⁵N), ²J(³¹P, ¹³C), and ²J(³¹P, ²⁹Si) were determined. Low temperature NMR spectra were measured for derivatives for which rotation about the P N bond at room temperature is fast, showing the presence of two rotamers at low temperature. The respective conformation of these rotamers could be assigned by ¹³C, ¹⁵N, and ³¹P NMR spectroscopy. Isotope‐induced chemical shifts ¹Δ^15/14N(³¹P) were determined for all compounds at natural abundance of ¹⁵N by using Hahn‐echo extended polarization transfer experiments. The molecular structure of 11 in the solid state reveals pyramidal surroundings of the nitrogen atom and mutual trans‐positions of the tert‐butyl groups at phosphorus and nitrogen. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:667–676, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10084     

15N NMR spectroscopy 24—chemical shifts and coupling constants of α-amino acid N-carboxyanhydrides and related heterocycles

The chemical shifts of amino acid N-carboxyanhydrides (NCAs) and cyclic or linear urethanes are less sensitive to solvent effects than those of amides and lactams. The values of the one-bond ¹⁵N? ¹H coupling constants depend on the solvent and are 5-8 Hz larger than those of ureas and amides. The ¹⁵N? ¹³C coupling constant of the N? CO group is also unusually high, while that of the N—CH group lies within the range known for N-acylated aliphatic amines. The one-bond ¹⁵N? ¹³C coupling constant was found to be insensitive to conformational changes.     

Nitrogen-15 coupling constants: Geminal coupling, 2J(15NH), in cis- and trans-aldonitrones and vicinal coupling, 3J(15NH), in cis-and trans-ketimines,oxaziridines and nitrones

Nitrogen-15-hydrogen ²J(¹⁵NH), ¹⁵N, ¹³C ¹J(¹⁵N¹³C) and ¹³C, H ¹J(¹³CH) coupling constants have been measured and their signs determined for cis-and trans-[9-anthryl(¹³C)methylene](²H₃)methylamine (¹⁵N)-oxide. Values of ²J(¹⁵NH) were of similar magnitude (～2 Hz) but were of opposite sign. The results are compared and contrasted with those reported for related imino and quaternary imino systems. Vicinal ³J(¹⁵NH) coupling constants have been measured in cis- and trans-¹⁵N-[1-(α-naphthyl)ethylidene]benzylamine and ¹⁵N-[1-(p-nitrophenyl)ethylidene]-t-butylamine and were found to be larger when the imino methyl group was cis to the nitrogen lone pair. The corresponding cis and trans ketonitrones formed by photoisomerization of the derived oxaziridines had ³J(¹⁵NH) values of c. 3.3 Hz. A study of the signs and magnitudes of observed and calculated ¹⁵N,H coupling constants for all of the ¹⁵N labelled imines, oxaziridines, imine N-oxides (nitrones) and similar model systems which were synthesized is described.     

15N chemical shifts and one bond 15N?1H coupling constants in simple amides

An indirect method is employed for determining the ¹⁵N parameters at the natural abundance level in a series of simple acyclic and cyclic amides. The one bond coupling constant, ¹J(¹⁵N¹H), and the ¹⁵N chemical shift are measured as a function of the carbonyl substituent group or the ring size and the nature of the solvent (CCl₄ or H₂O). These ¹⁵N parameters are related to the amide bond structure, the nitrogen configuration and possible intermolecular hydrogen bonding (amide-amide or amide-water).     

Correlation between 29Si-15N spin-spin coupling constants and the 15N-NMR chemical shifts in silatranes

A nonlinear correlation has been found between the ²⁹Si-¹⁵N spin-spin coupling constants and the ¹⁵N-NMR chemical shifts in silatranes. The dependence has been used to calculate corrections to the spin-spin coupling constant for the electronegativity of a substituent on the silicon atom. This has allowed the previously obtained data on the length and order of the N Si coordinate bond for silatranes in solutions to be refined.Translated from Khimiya Geterotisiklicheskikh Soedinenii, No. 5, pp. 701–703, May, 1989.     

Aminoderivate von α‐P4S3, α‐P4Se3 und P3Se4 – Daten und Analyse der 31P‐NMR‐Spektren in Lösungen

Amino Derivatives of α‐P₄S₃, α‐P₄Se₃, and P₃Se₄; Data and Analyses of their ³¹P NMR Spectra in Solution α‐P₄S₃I₂, α‐P₄Se₃I₂, and P₃Se₄I were reacted with primary and secondary amines in CS₂. The reaction yields exo‐exo isomeres of α‐P₄S₃L₂ and α‐P₄Se₃L₂, the N‐bridged compounds α‐P₄S₃L′ and P₃Se₄L, with L = NHR¹, NPhR², THC (R¹ = ^tBu, Ad, Ph, Flu, TPMP; R² = Me, Et, ⁱPr), and L′ = NR¹. The ³¹P NMR data of the compounds in CS₂ solution were measured. By the reaction of α‐P₄Se₃I₂ with primary amines NH₂^tBu and NH₂Ad in CS₂ an asymmetric isomer α‐P₄Se₃I_endo(NHR¹)_exo was observed for the first time in the ³¹P NMR spectra. The influence of the ligands L on the ³¹P NMR parameter of α‐P₄S₃L₂, α‐P₄Se₃L₂, and P₃Se₄L is discussed.     

15N chemical shifts and long-range 1H-15N coupling pathways of selected strychnos alkaloids

The Strychnos alkaloids have been the focal point of considerable synthetic and spectroscopic effort. We now report the ¹⁵N chemical shifts and long-range ¹H-¹⁵N coupling pathways of strychnine, brucine, and holstiine at natural abundance. Long-range coupling pathways were established using a gradient-enhanced HMQC sequence optimized for the observation of ¹H-¹⁵N long-range couplings.     

Carbon-proton coupling constants in α-chlorostyrene-α-13C

The two stereochemically distinct two-bond carbon-13- hydrogen coupling constants J(¹³C? CH), for α-chlorostyrene-α-¹³C have been shown to be of similar magnitude but opposite sign (?6.3 and +5.6 Hz). A simple additivity relationship which adequately reproduces all the reported J(¹³C? CH) values for chloroethylenes has been found.     

Correlation of substituted aromatic β‐diketones' characteristic protons chemical shifts with Hammett substituent constants

Influence of dibenzoylmethane's substituents in meta and para positions on chemical shift values of tautomers' characteristic protons was investigated in four solvents with ¹H NMR spectroscopy: acetone‐d₆, benzene‐d₆, CDCl₃ and deuterated dimethyl sulfoxide (DMSO‐d₆). It was proved that the influence of substituents on chemical shifts strongly depends on the kind of the solvent; the greatest changes were observed in benzene‐d₆ and the smallest in CDCl₃. In acetone‐d₆ and DMSO‐d₆, the influence of substituents on chemical shifts is similar and the most regular. It allowed a fair correlation of chemical shifts of para‐substituted dibenzoylmethane derivatives' characteristic protons with Hammett substituent constants in these solvents. In CDCl₃, characteristic protons' chemical shifts were near ¹H NMR spectroscopy measurement error limits, and, therefore, correlation with Hammett substituent constants in this solvent was unsatisfactory. In benzene, although the changes of chemical shifts are the most evident, the changes are also the most irregular, and, therefore, correlation in this solvent failed completely. Results of meta‐substituted derivatives were much more irregular, and their correlation with Hammett substituent constants was poor in all investigated solvents. Copyright © 2013 John Wiley & Sons, Ltd.     

Deuterium‐induced isotope effects on the 13C chemical shifts of α‐d‐glucose pentaacetate

1,2,3,4,6‐Penta‐O‐acetyl‐α‐d ‐glucopyranose and the corresponding [1‐²H], [2‐²H], [3‐²H], [4‐²H], [5‐²H], and [6,6‐²H₂]‐labeled compounds were prepared for measuring deuterium/hydrogen‐induced effects on ¹³C chemical shift ⁿΔ (DHIECS) values. A conformational analysis of the nondeuterated compound was achieved using density functional theory (DFT) molecular models that allowed calculation of several structural properties as well as Boltzmann‐averaged ¹³C NMR chemical shifts by using the gauge‐including atomic orbital method. It was found that the DFT‐calculated C–H bond lengths correlate with ¹Δ DHIECS. Copyright © 2013 John Wiley & Sons, Ltd.     

N1‐(4‐tert‐Butyl­phenyl)‐N2‐hydroxy‐α‐oxo‐α‐phenyl­acet­amidine and N2‐hydroxy‐N1‐(4‐nitro­phenyl)‐α‐oxo‐α‐phenyl­acet­amidine hemihydrate

In the title compounds, C₁₈H₂₀N₂O₂, (I), and C₁₄H₁₁N₃O₄·0.5H₂O, (II), respectively, the oxime groups have an E configuration. In (I), the mol­ecules exist as polymers bound by intermolecular C—H⋯O and O—H⋯N hydrogen bonds around inversion centres. In (II), intermolecular OW—H⋯N, OW—H⋯O and O—H⋯OW interactions stabilize the molecular packing.     

The Crystal and Molecular Structure of 3-Oxo-17β-acetoxy-Δ4-14α-methyl-8α, 9β, 10α, 13α-estrene

The crystal and molecular structure of 3-oxo-17β-acetoxy-Δ⁴-14α-methyl-8α, 9β, 10α, 13α-estrene, C₂₁H₃₀O₃, has been determined by X-ray diffraction analysis. The crystals belong to the orthorhombic space group P2₁2₁2₁, with the cell dimensions a = 12.093 Å, b = 19.667 Å, c = 7.746 Å; Z = 4. Intensity data were collected at room temperature with an automatic four-circle diffractometer. The structure was solved by direct methods and the parameters were refined by least-squares analysis. All the hydrogen atoms were included in the refinement. The final R value was 0.038 for 1413 observed reflections. The conformation of ring A is intermediate between a half-chair and a 1, 2-diplanar form. The hydrogens at C(9) and C(10) are anti, the B/C ring junction is trans, and rings B and C adopt chair conformations. Ring D is cis fused and is halfway between C₂ and C_s forms.     

Isotope‐induced chemical shifts 2Δ10/11B(29Si) in alkenylsilanes containing three‐ and four‐coordinate boron. A new tool for studying weak intramolecular boron–element bonds

Numerous alkenylsilanes with silyl and boryl groups in cis ‐positions at the C?C bond were studied for the first time by ²⁹Si NMR with regard to isotope‐induced chemical shifts Δ^10/11B(²⁹Si). Such effects are transmitted across an Si—X—B bridge (X = H, OR, SR, Cl) most efficiently if the interactions in this bridge are weak. In the absence of an Si—X—B bridge, ³Δ^10/11B(²⁹Si) effects were not observed. In such cases, where, depending on the substituents, both weak and strong B—X bonding are possible, the ²Δ^10/11B(²⁹Si) effects were readily observed only for weak B—X interactions (except for X = Cl), whereas for strong B—X bonding the effects were small or not detectable. Thus, the ²Δ^10/11B(²⁹Si) values provide another tool for probing weak interactions which are not clearly reflected by other NMR data. Copyright © 2002 John Wiley & Sons, Ltd.     

Carbon-13 chemical shifts of α,β-unsaturated acids

Carbon-13 spectra of 59 α,β-unsaturated carboxylic acids have been measured. Large differential shieldings of ethylenic carbons in the cis and trans isomers of acrylic acid derivatives were found (altogether 15 isomeric Z- and E-pairs of acids were investigated). The origin of differential shieldings is complex and both molecular ground states as well as changes in excited states appear to be involved. All measured ¹³C chemical shifts can be described by additive parameters that provide a straightforward new technique by which structural assignments can be made for a wide variety of isomeric mono-, di- and tri- substituted α,β-unsaturated acids.