Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.     

Extremes of nuclear structure

With the advent of medium and large gamma detector arrays, it is now possible to look at nuclear structure at high rotational forces. The role of pairing correlations and their eventual breakdown, along with the shell effects have showed us the interesting physics for nuclei at high spins — superdeformation, shape co-existence, yrast traps, alignments and their dramatic effects on nuclear structure and so on. Nuclear structure studies have recently become even more exciting, due to efforts and possibilities to reach nuclei far off from the stability valley. Coupling of gamma ray arrays with ‘filters’, like neutron wall, charged particle detector array, gamma ray total energy and multiplicity castles, conversion electron spectrometers etc gives a great handle to study nuclei produced online with ‘low’ cross-sections. Recently we studied, nuclei in mass region 80 using an array of 8 germanium detectors in conjunction with the recoil mass analyser, HIRA at the Nuclear Science Centre and, most unexpectedly came across the phenomenon of identical bands, with two quasi-particle difference. The discovery of magnetic rotation is another highlight. Our study of light In nucleus, 107In brought us face to face with the ‘dipole’ bands. I plan to discuss some of these aspects. There is also an immensely important development — that of the ‘radioactive ion beams’. The availability of RIB, will probably very dramatically influence our ‘conventional’ concept of nuclear structure. The exotic shapes of these exotic nuclei and some of their expected properties will also be touched upon.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Synthesis and characterization of vanadium(V)-phosphinimide complexes

Synthetic routes to vanadium(V)-phosphinimide derivatives are addressed. Initial synthetic efforts afforded the known compound formulated as VCl(2)(NPPh(3))(3) which was crystallographically determined to be the salt [VCl(NPPh(3))(3)]Cl (1). Reactions of the vanadium-imide precursors VCl(3)(NAr) (Ar = Ph, C(6)H(3)-2,6-iPr(2)) with R(3)PNSiMe(3) (R = Ph, iPr, tBu) afforded VCl(2)(NPh)(NPPh(3)) (4), VCl(2)(NPh)(NPiPr(3)) (5), VCl(2)(NPh)(NPtBu(3)) (6), VCl(2)(NC(6)H(3)-2,6-iPr(2))(NPPh(3)) (7), VCl(2)(NC(6)H(3)-2,6-iPr(2))(NPiPr(3)) (8), and VCl(2)(NC(6)H(3)-2,6-iPr(2))(NPtBu(3)) (9) in yields ranging from 72% to 84%. Subsequent alkylation or arylation reactions resulted in VMe(2)(NC(6)H(3)-2,6-iPr(2))(NPtBu(3)) (10), VPh(2)(NPh)(NPtBu(3)) (11), VPh(2)(NC(6)H(3)-2,6-iPr(2))(NPiPr(3)) (12), and VPh(2)(NC(6)H(3)-2,6-iPr(2))(NPtBu(3)) (13) while substitution reactions with Li[N(SiMe(3))(2)] and Li[SBn] gave VCl(N(SiMe(3))(2))(NPh)(NPtBu(3)) (14) and V(SBn)(2)(NC(6)H(3)-2,6-iPr(2))(NPtBu(3)) (15) in yields ranging from 40% to 49% yield. Polarization of the N-P phosphinimide bond and V-N multiple bond character are evidenced by crystallographic data.     

Syntheses and reactions of the bis-boryloxide O(Bpin)2(pin = O2C2Me4)

The reaction of the phosphine oxides, OPEt31 and OPn-Bu32 with pinacolborane (HBpin) results in phosphine oxide reduction and the formation of O(Bpin)23. In contrast, the phosphine oxide OPn-Bu3 reacts with HB(C6F5)2 or B(C6F5)3 to give only the donor-acceptor adducts. Compound 3 reacts with HNPt-Bu3 to give the phosphinimonium borate salt, [t-Bu3PNH2][(Bpin(OBpin)2]6, while reaction with Cp2ZrMe2 affords the species Cp2Zr(OBpin)27.     

Differentiation of neurons from neural precursors generated in floating spheres from embryonic stem cells

Background  

Neural differentiation of embryonic stem (ES) cells is usually achieved by induction of ectoderm in embryoid bodies followed by the enrichment of neuronal progenitors using a variety of factors. Obtaining reproducible percentages of neural cells is difficult and the methods are time consuming.     

Steric effects in metathesis and reduction reactions of phosphinimines with catechol- and pinacolboranes

A series of catecholboryl-phosphinimide complexes with the general formula (mu-(R(3)PN)Bcat)(x)() (cat = O(2)C(6)H(4)) have been synthesized via associative metathetical reactions. For R = Et, n-Bu, Ph, and i-Pr and R(3) = n-Bu t-Bu(2) X-ray crystallography as well as solution NMR spectroscopy and reactivity studies reveal that these species are dimeric. In the case of R = t-Bu, the steric congestion results in the monomeric species, t-Bu(3)PNBcat. Similarly, reactions of R(t-Bu)(2)PNH (R = n-Bu, t-Bu) and i-Pr(3)PNH with pinacolborane (HBO(2)C(2)Me(4) = HBpin) led to the formation of n-Bu(t-Bu(2))PNBpin, t-Bu(3)PNBpin, and i-Pr(3)PNBpin. Analogous reactions of smaller phosphinimines R(3)PNH (R = Et or n-Bu) with pinacolborane (HBpin) generated free phosphine and the boron-containing product HN(Bpin)(2). In the related reactions of R(3)PNPh or R(3)PNAd (R = Et and n-Bu) and HBpin, the white crystalline solids PhHN(Bpin) or AdHN(Bpin) were isolated. HN(Bpin)(2) was also derived from the reaction of Et(3)PNSiMe(3) and HBpin. Kinetic studies showed this reaction is first order in both reagents with a rate constant of 1.3(7) x 10(-4) s(-1). A mechanism involving a 1:1 donor-acceptor interaction of the phosphinimine and borane affording reduction of the phosphinimine to phosphine with concurrent formation of borylamine is proposed. Computational studies were performed to probe the steric effects on these reactions of phosphinimine and borane. Model reactions involving t-Bu(3)PNH showed a lower activation barrier for protonolysis in comparison to phosphinimine reduction. In contrast, for the smaller phosphinimine H(3)PNH, the activation barriers for phosphinimine reduction are lower. The causes of these steric effects are considered.     

Boron and aluminum complexes of sterically demanding phosphinimines and phosphinimides

Reactions of sterically demanding phosphinimines R3PNH [R=i-Pr (1), t-Bu (2)] were examined. Reactions with B(C6F5)3 formed the adducts (R3PNH)B(C6F5)3 [R=i-Pr (3), t-Bu (4)] in high yield. On the other hand, 2 reacts with HB(OBu)2, evolving H2 to give t-Bu3PNB(OBu)2 (5). The reaction of 2 equiv of 2 with BH3.SMe2 affords the species (t-Bu3PN)2BH (6). In contrast, the reaction of n-Bu(t-Bu)2PNH with BH3.SMe2 results in the formation of the robust adduct n-Bu(t-Bu)2PNH.BH3 (8). An alternative route to borane-phosphinimide complexes involves Me3SiCl elimination, as exemplified by the reaction of BCl2Ph with n-Bu3PNSiMe3, which gives the product n-Bu3PNBCl(Ph) (9). The corresponding reactions of the parent phosphinimines 1 and 2 with AlH3.NMe2Et give the dimers [(mu-i-Pr3PN)AlH2]2 (10) and [(mu-t-Bu3PN)AlH2]2 (11). Species 11 reacts further with Me3SiO3SCF3 to provide [(mu-t-Bu3PN)AlH(OSO2CF3)]2 (12). The reaction of the lithium salt [t-Bu3PNLi]4 (13) with BCl3 proceeds smoothly to give t-Bu3PNBCl2 (14), which is readily alkylated to give t-Bu3PNBMe2 (15). Subsequent reaction of 15 with B(C6F5)3 results in methyl abstraction and the formation of [(mu-t-Bu3PN)BMe]2[MeB(C6F5)3]2 (16). The reaction of 13 in a 2:1 ratio with BCl3 gives the salt [(t-Bu3PN)2B]Cl (17). This species can be methylated to give (t-Bu3PN)2BMe (18), which undergoes subsequent reaction with [Ph3C][X] (X=[B(C6F5)4], [PF6]) to form the related salts [(t-Bu3PN)2B][B(C6F5)4] (19) and [(t-Bu3PN)2B][PF6] (20), respectively. Analogous reactions with [Ph3C][BF4] afforded [t-Bu3PNBF2]2 (21). Compounds 3, 4, 6, 8, 11, 12, 17, 19, and 21 were characterized by X-ray crystallography.