Heteroatom derivatives of aziridine

Reaction of ethyleneimine with boron trichloride and tribromide below −20° C, with reactants in ratios 1∶1 and 2∶1, gives labile N-β-halo-genoethyl-substituted halogenoborazenes of the types XCH₂CH₂NHBX₂ and (XCH₂CH₂NH)₂BX (X = Cl, Br). These compounds decomposed spontaneously on coming to room temperature, with the evolution of HX and formation of substances whose compositions are, respectively C₂H₄NBX₂ and C₄H₉N₂BX₂. With a 3∶1 ratio of reactants the product is the relatively stable tris(β-halogenoethylamino)borane (XCH₂CH₂NH)₃ B (X = Cl, Br), which loses only one molecule of HX when heated under vacuum. For Part V see [1].     

Multiple bond migration with participation of a protophilic agent

The pathways of migration of the double bond in heteroallylic systems XCH₂CH=CH₂ (X =NMe₂, OMe, PMe₂, and SMe) with participation of hydroxide ion were investigated by theab initio RHF/6-31+G^* and MP2/6-31+G^* methods. The results are compared with those of analogous calculations of the systems with X=H, Me. Conformational isomerism of the initial molecules and reaction products, as well as the structure of intermediate carbanions, are considered. Increased acidity of compounds containing atoms of the third-row elements is explained in terms of a negative hyperconjugation model, 1,3-Hydrogen shift with participation of hydroxide ion in the system XCH₂CH=CH₂ results in double bond migration toward substituent X to form 1-hetero-1-propenes XCH=CHMe. Comparison of the energies of the final products indicates thermodynamic preferableness of the formation ofE-isomers. At the same time, in the case of substituents with atoms of the second-row elements the interaction of σ-bonds of the substituents and the p-AO of the terminal C atom additionally stabilizesZ-isomers of the carbanions and can be the reason for preferable kinetically controlled formation of these isomers. If the subsituents contain atoms of the third-row elements, the formation ofE-isomers of 1-hetero-1-propenes becomes both kinetically and thermodynamically predominant.     

A theoretical approach to substituent effects: Stabilities and conformational preferences in β-substituted ethyl radicals

Ab initio molecular orbital theory is used to study substituent effects in a series of β-substituted Et radicals XCH₂CH₂. For X = BH₂ (plan.), CH₃, NH₂, OH and F, only slight conformational preferences and weak stabilizations are indicated. Such behaviour may be rationalized, using a PMO model, in terms of opposing changes, accompanying variation in X, in positive and negative hyperconjugation between the XCH₂ group and the CH₂ centre. On the other hand, for groups containing an appropriately oriented, low-lying vacant orbital, viz. X = Li, BeH and BH₂ (perp.), there is a pronounced preference for the perpendicular conformation of the radical. This is attributed to 1,3-interaction between the singly-occupied 2p(C) orbital and the vacant 2p(X) orbital.     

Stereospecific Olefin Synthesis via Lithium Vinylcuprates

The conjugate addition of cis- or trans-1-alkenyl-cuprolithium complexes (R? CH?CH? )₂CuLi · X_n

1 R ? alkyl, X ? ligands such as ether, tetrahydrofuran, (CH₃O)₃P and (n-Bu)₃P. Physical studies to determine the structure of these copper reagents are in progress, see footnote ²⁰ of reference [1].

to α, β-unsaturated carbonyl compounds was found to occur with high retention of double bond geometry, affording isomerically pure cis- or trans-γ, δ-ethylenic carbonyl compounds. The same 1-alkenylcuprates also react stereospecifically with alkyl halides to give isomerically pure cis- or trans-olefins.     

The role of charge-site location in fragmenting ions. 1—[CH3 CHXCOOCH3]+˙ and [CH2XCH2 COOCH3]+˙ ions and the structures of daughter ions derived from the loss of X (X = I,Br, Cl and CH3)

The structures of the m/z 87, [C₄H₇O₂]⁺, ions generated by dissociative ionization of CH₃CGXCOOCH₃ and XCH₂CH₂COOCH₃ (X = CH₃, Cl, Br, and I) have been investigated via their unimolecular and collisionally activated fragmentations and by apperance energy measurements. For both precursors loss of X = CH₃ produced, via H atom transfer, ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_2 = CH}\mathop {\rm C}\limits^{\rm + } \left({{\rm OH}} \right){\rm OCH}_{\rm 3} $\end{document} (a), ΔH_f = 386 kj mol^?1. In marked contrast, loss of I^˙ from ionized CH₃CHICOOCH₃ and ICH₂CH₂COOCH₃ proceeded without rearrangement to yield respectively ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_3}\mathop {\rm C}\limits^{\rm + } {{\rm HCOOCH_3}} $\end{document} (b), ΔH_f = 480 kJ mol^?1 and (c), ΔH_f = 450 kJ mol^?1. These different fragmentation behaviours are explained via photoelectron spectra which show that the formal charge site in the precursor ion is at the carbonyl oxygen when X = CH₃ but at the halogen atom when X = I. The precursor molecules X = Cl and Br display both of the above characteristics, CH₃CHXCOOCH₃ yielding mixtures of a and b and XCH₂CH₂COOCH₃ producing a and c ions.     

A theoretical approach to substituent effects: Interaction between directly bonded groups in the isoelectronic series XNH3+, XCH3, and XBH3−

Ab initio molecular orbital theory including full geometry optimization at the 4-31G level is used to examine the interactions between substitutents X(X = Li, BeH, BH₂, CH₃, NH₂, OH and F) and substrates Y(Y = NH₃⁺, CH₃, BH₃^?) in the isoelectronic series XNH₃⁺, XCH₃ and XBH₃^?. The results indicate that the interaction energies are dominated by σ-effects. NH₃⁺ is found to interact favorably with the σ-donors (e.g. Li, BeH and BH₂) and unfavorably with the σ-acceptors (e.g. F, OH, NH₂). The reverse pattern a observed for XBH₃^?. The range of interaction energies for XCH₃ is considerably smaller than for XNH₃⁺ and XBH₃^?.     

Preparation and reactions of [2,2-bis(carbethoxy)propyl]cyclopentadienyldicarbonyliron

Although

, (Fp  η-C₅H₅Fe(CO)₂) (I) is stable and characterizable, the lower homologue FpCH₂CH(CO₂CH₃)₂ (II) is not; this we attribute to a facile elimination reaction resulting from the relatively acidic β-hydrogen of II. Formation of I from Fp^? and XCH₂CE₂CH₃ (X  Br, Cl; E  CO₂CH₂CH₃) and cleavage of its FeC bonds (using H⁺, Br₂, Ce^IV and Hg^II) occur without major amounts of ester group migrations, even though ·CH₂CE₂CH₃ radicals are involved in some of these reactions.     

Electron impact mass spectrometry of diethyl 2-oxysubstituted alkylphosphonates—a remarkably regiospecific α-cleavage

The major electron impact induced fragmentation of 2-hydroxyphosphonic esters, XCH₂CH(OH)CH₂PO₃Et₂ (and their O-derivatives) involves the C(2)–C(3) α-cleavage, yielding the XCH₂^· radical and the oxocarbonium ion, ⁺HO = CHCH₂PO₃Et₂. No evidence for a competitive C(1)–C(2) α-cleavage was obtained, and the results suggest a stabilizing effect of the phosphonyl group on the α-oxocarbonium system.     

Relation between the Length of the Transannular Bond Si←N in 1-Substituted Silatranes and the Inductive Effect of Substituents at the Silicon Atom

A strict linear correlation is found between the length of the coordination bond Si-N in 1-substituted silatranes XCH₂Si(OCH₂CH₂)₃N and the inductive constant _I of substituent XCH₂. This equation is also valid for other compounds of the RSi(OCH₂CH₂)₃N type, in which silicon is bound to an sp ²-carbon atom (R = CH = CH₂, Ph, 2-furyl, 2-thienyl, etc.). The deduced correlation equation allows determination of earlier unknown and refinement of existing _4I constants of substituents R on the basis of X-ray diffraction Si-N bond lengths in silatranes RSi(OCH₂CH₂)₃N. Deviations from the correlation point to noninductive interaction between substituent R and the silantranyl group (R = R'O). The bond length in 1-fluorosilatrane nicely fits the deduced equation.     

Radicals containing β-muonium and α or β substituents:

A range of radicals, CH₂(Mu) HX (1) and XCH(Mu)CR₂ (2), where X is a second-row substituent, have been studied by transverse-fieldμ ⁺SR spectroscopy. The reduced muon—electron hyperfine coupling constants (A′_Mu) for class (1) were all close to 37.3 G, the value for the parent radical CH₂(Mu)CH₂. However, for class (2)A′ _Mu values are greatly reduced, as is the case for the corresponding hydrogen derivatives, XCH₂CR₂, relative to CH₃CH₂. Nevertheless, the reduction in coupling for Mu in (2] is appreciably less that that for¹H in XCH₂CR₂ radicals, suggesting significant competition between Mu and X for the out-of-plane site. In addition to theμ ⁺ SR studies, the ESR spectra for the radicals (MeO)₃SiCHCH₃ and (MeO)₃SiCH₂CH₂ have been measured for comparative purposes.     

Hetero‐π‐systems from 2 + 2 cycloreversion,part 2.1Ab initio thermochemical study of heterocyclobutanes 2 + 2 cycloreversion to form heteroethenes H2C=X (X=NH,O, SiH2, PH,S)

Ab initio and DFT thermochemical study of diradical mechanism of 2 + 2 cycloreversion of parent heterocyclobutanes and 1,3‐diheterocyclobutanes, cyclo‐(CH₂CH₂CH₂X), and cyclo‐(CH₂XCH₂X), where X = NH, O, SiH₂, PH, S, was undertaken by calculating closed‐shell singlet molecules at three levels of theory: MP4/6‐311G(d)//MP2/6‐31G(d)+ZPE, MP4/6‐311G(d,p)//MP2/6‐31G (d,p)+ZPE, and B3LYP/6‐311+G(d,p)+ZPE. The enthalpies of 2 + 2 cycloreversion decrease on going from group 14 to group 16 elements, being substantially higher for the second row elements. Normally endothermic 2 + 2 cycloreversion is predicted to be exothermic for 1,3‐diazetidine and 1,3‐dioxtane. Strain energies of the four‐membered rings were calculated via the appropriate homodesmic reactions. The enthalpies of ring opening via the every possible one‐bond homolysis that results in the formation of the corresponding 1,4‐diradical were found by subtracting the strain energies from the central bond dissociation energies of the heterobutanes CH₃CH₂—CH₂XH, CH₃CH₂—XCH₃, and HXCH₂—XCH₃. The latter energies were determined via the enthalpies of the appropriate dehydrocondensation reactions, using C—H and X—H bond energies in CH₃XH calculated at G2 level of theory. Except 1,3‐disiletane, in which ring‐opening enthalpy attains 69.7 kcal/mol, the enthalpies of the most economical ring openings do not exceed 60.7 kcal/mol. The 1,4‐diradical decomposition enthalpies found as differences between 2 + 2 cycloreversion and ring‐opening enthalpies were negative, the least exothermicity was calculated for ⋅ CH₂SiH₂CH₂CH₂. The only exception was 1,3‐disiletane, which being diradical, CH₂SiH₂CH₂SiH₂, decomposed endothermically. Since decomposition of the diradical containing two silicon atoms required extra energy, raising the enthalpy of the overall reaction to 78.9 kcal/mol, 1,3‐disiletane was predicted to be highly resisting to 2 + 2 cycloreversion. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:704–720, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20377     

Effect of pressure on the conformational equilibrium of 2-haloethanol in carbon disulfide

IR spectra of 2-haloethanols (CH₂XCH₂OH, X = Cl, Br, and I) in carbon disulfide were measured at 25°C up to 2.5 kbar. The volume changes accompanying the transformation to the Gg conformer of the compounds were ?1.2, +0.5, and +1.3 cm³ mol^?1 for X = Cl, Br, and I, respectively.     

On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels–Alder Reactions

Intramolecular Diels–Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6‐31+G(d) and CBS‐QB3 levels of theory for a series of 1,3,8‐nonatrienes, H₂C?CH? CH?CH? CH₂? X? Z? CH?CH₂ [? X? Z? =? CH₂? CH₂? ( 1 ); ? O? C(?O)? ( 2 ); ? CH₂? C(?O)? ( 3 ); ? O? CH₂? ( 4 ); ? NH? C(?O)? ( 5 ); ? S? C(?O)? ( 6 ); ? O? C(?S)? ( 7 ); ? NH? C(?S)? ( 8 ); ? S? C(?S)? ( 9 )]. For each system studied ( 1 – 9 ), cis‐ and trans‐TS isomers, corresponding, respectively, to endo‐ and exo‐positioning of the ? C? X? Z? tether with respect to the diene, have been located and their relative energies (E_rel^TS) employed to predict the cis/trans IMDA product ratio. Although the E_rel^TS values are modest (typically <3 kJ mol^?1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (X?O→NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis‐TS, namely (1) unfavorable torsional (eclipsing) strain about the C4? C5 bond, that is caused by the ? C? X? C(?Y)? group’s strong tendency to maintain local planarity; and (2) attractive electrostatic and secondary orbital interactions between the endo‐(thio)carbonyl group, C?Y, and the diene. The former interaction predominates when X is weakly electronegative (X?N, S), while the latter is dominant when X is more strongly electronegative (X?O), or a methylene group (X?CH₂) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1 , 2 , 3 , and 4 (published work) and 5 , 6 , and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans‐selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14 , which undergoes a more trans‐selective IMDA reaction than the corresponding ester tethered precursor 13 .     

1,1-Dimethyl-1-(trialkoxysilylmethyl)hydrazinium and 1,1-Dimethyl-1-(silatranylmethyl)hydrazinium Halides

Formerly unknown 1,1-dimethyl-1-(trialkoxysilylmethyl)- and 1,1-dimethyl-1-(silatranylmethyl)hydrazinium halides were prepared by reaction of 1,1-dimethylhydrazine with (halomethyl)trialkoxysilanes XCH₂Si(OR)₃ (X = Cl, I; R=Me, Et) and 1-(halomethyl)silatranes XCH₂Si(OCH₂CH₂)₃N (X = Cl, Br). 1,1-Dimethyl-1-(silatranylmethyl)hydrazinium chloride and iodide were also obtained by transetherification of corresponding 1,1-dimethyl-1-(trimethoxysilylmethyl)hydrazinium halides with tris(2-hydroxyethyl)amine.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005, pp. 915–919.Original Russian Text Copyright © 2005 by Sorokin, Voronkov.     

Synthesis of [?CH2C(CO2Et)2CH2Ar?]n polymers and their unique optical properties by through‐space interactions between Ar and CO groups

Polymers of type [? CH₂C(CO₂Et)₂CH₂Ar? ]_n (Ar = 1,4‐phenylene, 2,6‐naphthylene, 9,10‐anthrylene, or 1,4‐phenylene‐ethynylene‐1,4‐phenylene) were synthesized by alkylation of diethyl malonate with XCH₂ArCH₂X (X = Cl or Br). These polymers exhibited unexpectedly enhanced UV absorption and strong, broad, bathochromically shifted fluorescence spectra compared with the parent Ar compounds. The origin of these photophysical characteristics was postulated to be a configuration interaction between the π→π* excitation of the aromatic moiety and the n→π* excitation of the carbonyl moiety on the trimethylene tether via intramolecular charge transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The nature of the super-electron-releasing inductive effect of the silatranyl group and its spectroscopic and chemical consequences

The relationship between the structure of carbofunctionally substituted 1-methylsilatranes XCH₂Si(OCHRCH₂)₃N (R = H, Me; X = R"₂N, R"S, Cl, etc., R" = Alk), the unusually high electron-releasing properties of the silatranyl group, and the enhanced chemical reactivity of the exocyclic XCH₂ substituent is discussed.     

α,ω-Bis(4-substituted-3-quinolinylthio)alkanes from reactions of thioquinanthrene with alkoxides

The reaction of thioquinanthrene 1 with sodium alkoxides and α,ω-dihaloalkanes leads to the formation of α,ω-bis[4-(4-methoxy-3-quinolinylthio)-3-quinolinylthio]alkanes 4 . The yield depends on the nature of α,ω-dihalo-alkanes. The effect of α,ω-dihaloalkanes of the following types: XCH₂X (X = Cl,Br,I), X(CH₂)₂X (X = Cl,Br,I), Br(CH₂)₃Br and Br(CH₂)₆Br were studied. The preparation of 4-alkoxy-3′-(ω-bromoalkylthio)-3,4′-diquinolinyl sulfide 3 and their transformation to α,ω-bis(4-alkoxy-3-quinolinylthio)alkanes 6 were studied as well.     

Zur synthese und struktur von pentacarbonylmetall(0)-Komplexen intramolekular basenstabilisierter zinn(III)-verbindungen

The synthesis and structure of pentacarbonylmetal(0) complexes of the types (C0)₅MSn(XCH₂CH₂)₂E (M = Cr, Mo, W; X = O, S; E = NR, PPh, O, S) and (CO)₅ WSn(SCH₂CH₂)₂E · py (E = NMe, O, S) are reported.¹¹⁹Sn and ¹³C NMR studies show the compounds with X = O and E = NR to be dimeric whereas the derivatives with X = S have been found to be monomeric. The π-acceptor behaviour of the ligands Sn(XCH₂CH₂)₂E is comparable to that of the phosphanes. The barriers to internal rotations about the nitrogencarbon bonds have been determined for the NBu^t derivatives.     

Schwingungsspektroskopische Untersuchungen an den Organohydrogensilanen (XCH2)(CH3)2SiH (X = Cl,Br, J), X(YO)2SiH (X = CH3, C2H5/Y = CH3, C2H5 … tert.-C4H9), (C6H5)2SiH2 und C6H5SiH3

Infrared and Raman Spectroscopic Investigations on the Organosubstituted Silicon Hydrides (XCH₂)(CH₃)₂SiH (X = Cl, Br, J), X(YO)₂SiH (X = CH₂, C₂H₅/Y = CH₃, C₂H₅ … tert.-C₄H₉), (C₆H₅)₂SiH₂ and C₆H₅SiH₃ Typical band splittings, specially for the SiH stretching vibration, are shown in the infrared and Raman spectra of the silicon hydrides (XCH₂)(CH₃)₂SiH (X = Cl, Br, J), and X(YO)₂SiH (X = CH₃, C₂H₅/Y = CH₃, C₂H₅ … tert.-C₄H₉). The cause of this behavior is in all probability the existence of rotational isomers. Raman polarization measurements at organosubstituted silicon di- and trihydrides demonstrate the accidental degeneracy of the SiH valence vibrations.