CH2Cl Group Research Articles

The effects of β-alkoxy substituents on radical reactions: halogen-atom abstraction from alkyl chlorides

EPR spectroscopy has been used to measure the relative rates of halogen-atom abstraction from RCH2Cl [R = Pr, MeOCH2, (MeO)2CH, (MeO)3C, Me3Si] by the metalloid-centred radicals Me3N→ḂHBu, Et3N→ḂH2 and Et3Si˙(M˙) in cyclopropane and in oxirane solvents at 160–260 K. β-Methoxy substituents increase the rate of reaction, especially for chlorine abstraction by the highly nucleophilic amine–boryl radicals. The accelerating influence of the β-oxygen substituents is attributed to a polar effect which operates in the transition state and involves charge transfer from M˙ to the CH2–Cl group. The relative reactivities of the cis- and trans-isomers of 5-chloro-2-tert-butyl-1,3-dioxane indicate that the substituent effect of a β-alkoxy group does not depend markedly on the orientation of the β–C–O bond with respect to the rupturing C–Cl bond. It is concluded that the β–C–O bond dipole interacts electrostatically through space with the dipolar C ⋯ Cl ⋯ M grouping in the transition state and thus stabilises the latter relative to the reactants. This interpretation is supported by the results of ab initio molecular calculations for model systems. The EPR spectra of the β-alkoxyalkyl radicals are discussed in relation to their preferred conformations as deduced on the basis of the Heller–McConnell equation. The applicability of the latter equation is confirmed by ab initio calculations for the ethyl radical.

Power spectra as a diagnostic tool in probing statistical/nonstatistical behavior in unimolecular reactions

The possibility of utilizing different types of power spectra obtained from classical trajectories as a diagnostic tool to identify the presence of nonstatistical dynamics is explored by using the unimolecular bond-fission reactions of 1,2-difluoroethane and the 2-chloroethyl radical as test cases. In previous studies, the reaction rates for these systems were calculated by using a variational transition-state theory and classical trajectory methods. A comparison of the results showed that 1,2-difluoroethane is a nonstatistical system, while the 2-chloroethyl radical behaves statistically. Power spectra for these two systems have been generated under various conditions. The characteristics of these spectra are as follows: (1) The spectra for the 2-chloroethyl radical are always broader and more coupled to other modes than is the case for 1,2-difluoroethane. This is true even at very low levels of excitation. (2) When an internal energy near or above the dissociation threshold is initially partitioned into a local C–H stretching mode, the power spectra for 1,2-difluoroethane broaden somewhat, but discrete and somewhat isolated bands are still clearly evident. In contrast, the analogous power spectra for the 2-chloroethyl radical exhibit a near complete absence of isolated bands. The general appearance of the spectrum suggests a very high level of mode-to-mode coupling, large intramolecular vibrational energy redistribution (IVR) rates, and global statistical behavior. (3) The appearance of the power spectrum for the 2-chloroethyl radical is unaltered regardless of whether the initial C–H excitation is in the CH2 or the CH2Cl group. This result also suggests statistical behavior. These results are interpreted to mean that power spectra may be used as a diagnostic tool to assess the statistical character of a system. The presence of a diffuse spectrum exhibiting a nearly complete loss of isolated structures indicates that the dissociation dynamics of the molecule will be well described by statistical theories. If, however, the power spectrum maintains its discrete, isolated character, as is the case for 1,2-difluoroethane, the opposite conclusion is suggested. Since power spectra are very easily computed, this diagnostic method may prove to be useful.

On the Persistence of Molecular Symmetry in the Solid State and the Role of Molecular Group Dipole Moments. Centrosymmetry in Bis‐(Chloromethyl)benzenes

AbstractThe crystal structures and the 35Cl NQR spectra of 1,4‐bis(chloromethyl)‐2,3,5,6‐tetrachlorobenzene, 1,4‐(CH2Cl)2C6Cl4; 1,4‐bis(chloromethyl)‐2,3,5,6‐tetramethyl‐benzene, 1,4‐(CH2Cl)2C6(CH3)4; 1,4‐bis(chloromethyl)benzene, 1,4‐(CH2Cl)2C6H4; 1,2‐bis(chloromethyl)benzene, 1,2‐(CH2Cl)2C6H4 are reported. – The compounds 1,4‐(CH2Cl)2C6Cl4 and 1,4‐(CH2Cl)2(CH3)4 are isostructural, space group C–P1, Z = 1. 1,4‐(CH2Cl)2C6Cl4: a = 893.1(4) pm, b = 655.1(3) pm, c = 494.5(2) pm, α = 98.32(2)°, β = 96.87(2)°, γ = 103.60(2) 92°; 1,4‐(CH2Cl)2C6(CH3)4: α = 902.3(4) pm, b = 809.4(4) pm, c = 442.5(2) pm, α = 87.38(2)°, β = 83.02(2)°, γ = 65.00(2)°. 1,4‐(CH2)2C6H4 crystallizes monoclinic, C–P21/c, Z = 2, a = 848.8(4) pm, b = 465.0(2) pm, c = 1042.2(5) pm, β = 99.21(2)°. 1,2‐(CH2Cl)2C6H4 is noncentrosymmetric, orthorhombic, C–Fdd2, Z = 8, a = 1562.0(4) pm, b = 1358.0(3) pm, c = 790.4(2) pm. – The 35Cl NQR spectra of 1,4‐(CH2Cl)2C6(CH3)4, 1,4‐(CH2Cl)2C6H4, and 1,2‐(CH2Cl)2C6H4 are singlets, with negative temperature coefficients dν(35Cl)/dT over the temperature range 77 K–Tmelt and the frequencies are in the range 34.4 ≥ ν(35Cl)/MHz ≥ 31.8. 1,4‐(CH2Cl)2C6Cl4 shows a 35Cl NQR triplet, with negative temperature coefficients for 77 ≤ T/K ≤ 420, 37.5 ≥ ν(35Cl)/MHz ≥ 33.8, too. In this compound a phase transition occurs, with a wide hysteresis, Tc, up = 366 K, Tc, down = 328 K. The inductive effect on the 35Cl NQR in the CH2Cl group is strong. – In molecular crystals the complete symmetry of the free molecule seldom persists in the solid state. The molecular symmetry in the condensation process is fully or partially lost due to the van der Waals interaction of neighboring molecules. The compensation of the partial dipole moments of the two chloromethyl group in para position retains the molecular symmetry Ī in the solid phases. It will be discussed that in benzene derivatives either Ī, m or 2 are the “hard” symmetry elements, preserved in the solid state.

Dynamic and structural studies on 1,2,3-trichloropropane in the solid phase

35Cl nuclear quadrupole resonance (NQR) frequencies nu Q and spin-lattice relaxation times T1 were measured between 100 and 250 K in 1,2,3-trichloropropane (CH2ClCHClCH2Cl). Three narrow lines were detected in the stable solid phase, indicating that only one of the six possible conformers is present. Also, the three lines were assigned to the three chlorine atoms in the molecule from their distinct temperature behaviours. The dominant mechanism responsible for the relaxation above 200 K is proposed to be the reorientational motion of the CH2Cl end groups, and activation energies of 32.5 and 49.0 kJ mol-1 are determined for the two end groups. The 1H nuclear magnetic resonance lineshape f(H) shows a structure due to the dipolar interaction between the protons of the CH2Cl groups. From the analysis of f(H) a distance dHH=1.68 AA is obtained, which turns out to be quite close to that already determined in solid dichloroethane. Fast cooling of the sample from the liquid state produces very broad NQR signals. The results of differential thermal analysis seem to indicate the existence of a glassy state with a characteristic Tg=144 K.

Studies on structure–reactivity in the reaction of OH radicals with substituted halobenzenes in aqueous solutions

The reaction of OH radicals with a number of substituted halobenzenes (C6H5 –nXnY, where X = F, Cl or Br and Y = CH3, CH2Cl, CHCl2, CF3 or OCH3) produces a transient absorption band whose λmax is in the range 310–340 nm. This band is assigned to the OH adduct and decayed with second-order kinetics, the bimolecular rate constant being in the region of 0.6 × 109– 5.0 × 109 dm3 mol–1 s–1. The OH radical reacts mainly by addition to the benzene ring. The rate constants for the reaction of OH radicals, as determined from formation kinetics studies, are between 1.7 and 9.3 × 109 dm3 mol–1 s–1, and are found to depend on the nature of the substituents. A linear correlation is observed with the Hammett parameter. The distribution pattern for the OH adduct is discussed. The OH adduct can be oxidized by K3[Fe(CN)6]. The rate constant for the oxidation depends on the position of OH addition and the extent of oxidation on the nature of the substituents. The reaction of O– with 2-chlorotoluene is by H-atom abstraction (14%), producing an absorption band with λmax= 258 nm, and by addition to the benzene ring (86%), producing absorption bands at 290, 320 and 410 nm. The bimolecular rate constant for the reaction of O– with 2-chlorotoluene is 2.0 × 109 dm3 mol–1 s–1 and Iµ320nm= 2.6 × 103 dm3 mol–1 cm–1. For the reaction of eaq– with 2-chlorobenzyl chloride, 44% of the eaq– react with the Cl of the CH2Cl group producing an absorption band at 258 nm and 56% react with the Cl of the benzene ring producing an absorption band at 320 nm. The bimolecular rate constant as determined from the decay of eaq– is 2.2 × 1010 dm3 mol–1 s–1.

Reaction of ?,?,?-trichloro- and ?,?,?,?-tetrachloroalkanes with alkali metal acylates in aprotic solvents

Polychloroalkanes and -alkenes R(CH2)nCl (R=CHCl2CH2, CCl2=CH, n=1, 3) in dipolar aprotic solvents — dimethylformamide (DMF), dimethylsulfoxide (DMSO), hexamethylphosphoramide (HMPA) — at 130–150°C react selectively at the CH2Cl group with salts of carboxylic acids R′CO2K(Na) to form dichloroesters R′CO2· (CH2)nR (R=CHCl2CH2, CCl2=CH). In tetrachloroalkanes CCl3CH2(CH2)nCl (n = 1, 3, 5) under the same conditions the selectivity of the CCl3 and CH2Cl groups relative to the nucleophile R′CO2K(Na) is altered — unsaturated esters R′CO2(CH2)nCH=CCl2 are formed in one stage with yields of 75–90%. Under the selected conditions, high conversion of polychloroalkanes to esters is attained 3 to 5 times more rapidly than in acid media. The structure of the ester obtained has been confirmed by their PMR spectra.

Investigations on the curing of epoxides with phthalic anhydride

AbstractThe anhydride curing of epoxides was studied by performing copolymerizations of epichlorohydrin, phenyl glycidyl ether (PGE), or bisphenol‐A‐diglycidyl ether (BADGE) with phthalic anhydride (PSA). As initiators, tertiary amines or ammonium salts were used. In the case of epichlorohydrin, linear polyesters were obtained at 100°C. At higher temperatures (140–160°C), a side reaction of the CH2Cl group took place which caused branching and partial crosslinking of the polymer. The reaction of phenyl glycidyl ether with phthalic anhydride gave linear, strongly alternating copolymers at temperatures of 120–160°C. Molecular weights (M¯n) were in the range of 4000–87,000, depending on the purity of the starting materials and the initiator used. The reaction of the diepoxide BADGE with phthalic anhydride yielded highly crosslinked products. Their crosslink densities (which correlate with the glass transition temperature Tg). however, did not show the same dependence on initiator and purity of the starting materials as the molecular weights of the linear polyesters obtained by the “model reaction” of PGE with PSA. Possible reasons for this effect are discussed.

A computational analysis of the electrostatic potentials and relative bond strengths of hydrazine and some of its 1,1‐dimethyl derivatives

AbstractWe have carried out a computational study of hydrazine and five of its 1,1‐dimethyl derivatives, focusing on their electrostatic potentials and relative bond strengths. Our approach has involved the calculation of ab initio self‐consistent‐field molecular orbital wave functions and molecular properties using the GAUSSIAN 82 system of programs. The electrostatic potentials of the hydrazines possess negative regions of varying sizes and strengths associated with the nitrogens of the α‐diamino linkages. Through an analysis of the positions of the most negative potentials of these regions, we have obtained directly the dihedral angles between the nitrogen lone pairs in these systems. Our use of the electrostatic potential to obtain these angles is a direct and general approach, in contrast to indirect procedures used in the past. We find this dihedral angle to be close to 90° in hydrazine, with variations in the substituted hydrazines that depend on the nature of the substituents. A highly polar structure is found for 1‐chloromethyl‐1‐methylhydrazine, which involves a delocalization of electronic charge from the substituted nitrogen towards the CH2Cl group. We find that substituents able to withdraw significant amounts of electronic density from the central nitrogen lone pair regions, either through resonance or by induction, have a slight bond strengthening effect on the central N‐N bond. This is attributed to a decrease in the repulsion between the weakened nitrogen lone pair regions. The difficulties encountered in seeking the controlled oxidation of hydrazine to nitro derivatives may be due, in part, to the fact that two factors which would favor this, highly negative nitrogen potentials and strong N‐N bonds, are opposing in nature.

Influence of structure on the photo-degradation of PVC. Part IV—A conclusive approach to the mechanism of photo-oxidation and photo-dehydrochlorination

The photo-oxidation and the photo-dehydrochlorination of a series of PVC samples having different isotactic contents have been studied in the presence of oxygen. The build-up of carbonyl groups was found to decrease as the isotactic content was increased. Conversely, the dehydrochlorination quantum yield appeared to increase linearly as the isotactic content increased. It is proposed that the former result is due to a less favoured hydrogen abstraction reaction at the isotactic triads, resulting from a higher shielding of the hydrogen atoms at CHCl groups. The latter result is associated with both the occurrence of some chlorine atoms of low dissociation energy located at a definite type of isotactic triad and the favoured hydrogen abstraction reaction at the CH 2 group in syndio and heterotactic triads. The conclusions are discussed on the basis of the local conformations of the various triads. In particular, the role of the isotactic GTTG − triad conformation in the mechanisms above is emphasized.

Vibrational spectra and conformational analysis of chloromethylformate

The results of an IR and Raman study of normal chloromethylformate, HCOOCH 2Cl, and the deuterated derivative HCOOCD 2Cl are reported. A minor alteration to the assignments previously published is proposed. It was observed that this molecule exhibits two different crystalline phases, the IR spectra of which show pronounced polarisation effects. These dichroic spectra, however, give no information on the molecular conformation of crystalline chloromethylformate. The (s- cis,gauche) conformation of gaseous CMF was established by harmonic rigid rotor asymmetric top simulation of the IR vapour phase contours. No evidence was found for free or nearly free internal rotation of the CH 2Cl group, which was suggested by previous ab initio calculations.

13C and 1H NMR analysis of structural defects in PVC: Application to the production of defects at various polymerization stages

AbstractHigh resolution 1H and 13C NMR data were obtained on PVC and PVC reduced with Bu3SnH. The reduction is never complete and CH2Cl groups preferentially remain. It causes almost complete formation of cyclopentane structures from both internal and chain end unsaturation. 1H NMR gives total unsaturation as well as chain end unsaturation except if there are interferences with initiator residues; in that case, its combination with 13 C NMR of reduced PVC gives the chain end unsaturation. By the last method short branches and long ends are determined. Residual primary chlorine in all kinds of branches (methyl, ethyl, butyl, long ends) is taken into account. Long end contents are to be corrected (factor around 1.5), due to incomplete relaxation in standard analysis conditions. 1H NMR of reduced PVC can be used to get the total non‐reduced structures, both ‐CH2Cl and ‐CHCl‐. PVC was prepared by suspension or solution (trichlorobenzene) polymerization at 55° C, using dicetyl peroxydicarbonate as an initiator. The initiator residue content is higher in suspension PVC at very low conversion, and then levels off at a low value; in solution polymerization, it chiefly depends on the monomer/initiator ratio. At low conversion, more chain end and less short branches are present in suspension polymerization. Otherwise, only the butyl branch content shows a definite trend to increase with conversion. In solution polymerization, the number of defects is chiefly dependent on the initial monomer concentration; it is generally much higher than in suspension, except for the chloromethyl branches where both processes give about the same results.

Fluorescence properties of benzyl chloride in the vapor phase

The fluorescence and fluorescence-excitation spectra of benzyl chloride vapor have been observed at room temperature and in a supersonic jet. The fluorescence shows a structured spectrum with a quantum yield of 5 × 10 −5 upon excitation at the 0-0 band of the S 1←S 0 absorption. The fluorescence quantum yield in the S 1 region depends markedly on the excitation levels involving some internal rotation levels of the CH 2Cl group.

Influence of chlorination of poly(vinyl chloride) on miscibility with poly(methyl methacrylate)

The improvement of the miscibility of poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) with moderate chlorination of PVC was demonstrated by determination of cloud-point curves and glass transitions of the mixtures. Heats of mixing of low-molar-mass analogues for PMMA and for the various structural units present in chlorinated PVC (CPVC) were determined in a microcalorimeter along with Fourier transform infra-red spectroscopy of these mixtures. The results show that the improvement of miscibility is caused by a specific interaction between the carbonyl group of PMMA and predominantly the CHCl group of CPVC. The specific interactions present in these systems are best described as a Lewis acid-base type of interaction, considering the carbonyl oxygen of the ester as an electron donor and the hydrogen of the CHCl group as an electron acceptor: CO … HCCl. The decrease in miscibility observed when more strongly chlorinated PVC is used can be ascribed to the relatively high concentration of CCl 2 groups, which have a less favourable interaction with the carbonyl groups.

Relationship between the structure and the properties of carbohydrates in aqueous solutions: Sweetness of chlorinated sugars

The structural basis of the sweet taste of d-galactose, d-glucose, d-mannose, sucrose, and some of their chlorinated derivatives has been derived from an interpretation of their F.t.-i.r. spectra. AH-B glucophores are proposed in the light of the observed OH vibrations, and an explanation of the differences in sweetness of the monosaccharides is proposed. The hydrophobic character of the CH 2Cl, “γ” centre in the tripartite template does not seem to play the same role in monosaccharides and 4,1′,6′-trichloro-4,1′,6′-trideoxy- galacto-sucrose. The enhancement of sweetness in the disaccharide derivative is due to the enhanced hydrophobicity of the CH 2Cl groups as well as to specific interactions with water. A sharp i.r. absorption characteristic of free hydroxyl is found in the spectra of most of the very sweet polyhydroxy compounds.

Study of the molecular mobility in swollen poly(epichlorohydrin) 1. Nonpolar swelling agent

The broad line n.m.r. spectra of the amorphous fraction of poly(epichlorohydrin) have been analysed. Two motional transitions were observed and the T g and a low temperature transition β assigned to the motion of the CH 2Cl groups. The study of the poly(epichlorohydrin) swollen by a low molecular weight liquid (deuterobenzene), has provided information about the influence of swelling on the molecular dynamics, and the participation of intermolecular interactions in the second moment of the resonance lines. The observed value of the second moment of the spectra is higher than that calculated for a planar chain conformation. This indicates that the chain conformation of the atactic, amorphous poly(epichlorohydrin) is different from the conformation observed in the crystalline, isotactic fraction of the polymer.

Secondary kinetic isotope effects in hydrogen and deuterium abstraction by chlorine atoms from the chloromethyl group in gaseous ethyl chlorides: effects of isotopic substitution in the adjacent methyl group

Ground state chlorine atoms have been generated photochemically to study the attack on hydrogen in the CH 2Cl group, or deuterium in the CD 2Cl group, as a function of deuterium substitution in the vicinal methyl group of a number of ethyl chloride molecules. The experiments were carried out in the gas phase, at temperatures 9–95°C, using methane as competitor ( k r). Rate constants for the following reactions are reported: ▪ The temperature dependences of the relative rate constants k i/ k r were found to obey the Arrhenius rate law: ▪

Stereochemistry of rings, XV. γ-Lactone derivatives: Part 9. X-ray structure of 5-chloromethyl-2-oxazolidinone

C 4H 5NO 2Cl ( M r = 135.55) crystallizes in the monoclinic system, space group P2 1 ie with a = 9.257(2), b = 5.181(3), c = 12.620(2) A, β = 110.75(4)°, V = 566.0(4) A 3, Z = 4, D c = 1.59 g cm −1, μ(Cu Kα) = 53.16 cm −1, γ = 1.5418 A, F(000) = 280. The oxazolidinone ring is approximately planar; the geometrical parameters reveal a certain degree of electronic delocalization in the molecule. The CH 2Cl group assumes an axial position. The molecules are joined in dimers by strong N—H ⋯.. O hydrogen bonds.

The stabilities of Meisenheimer complexes. Part 33. Kinetic studies of the formation of isomeric σ-adducts from 2,4,6-trinitrobenzyl chloride and aliphatic amines in dimethyl sulphoxide

Kinetic and equilibrium data are reported for the reversible colour-forming reactions of 2,4,6-trinitro-benzyl chloride with some aliphatic amines in dimethyl sulphoxide and are compared with data for reactions of 1,3,5-trinitrobenzene. With n-butylamine and benzylamine three processes are observable : attack at the 3-position, attack at the 1-position, and transfer of a side-chain proton. For piperidine and pyrrolidine only two-of these are observable, attack at the 1-position being disfavoured for steric reasons. The formation of anionic σ-adducts occurs via zwitterionic intermediates and it is shown that the proton-transfer step may be kinetically significant. Reductions of rate constants for proton-transfer below the values expected for diffusion-controlled reaction are attributed to steric effects which are increased when reaction involves secondary amines and when the CH2Cl group is at the reaction site. Specific effects of chloride ions are noted and are attributed to their interaction with substituted ammonium ions.

Reaction of ?,?,?-trichloroalkenes with 1,1,1-trichloroethane and 1,1,1,3-tetrachloropropane, accompanied by rearrangement of radicals

In the reaction of CCl3CH3 with CCl2=CHCH2CH2CH2Cl, and of CCl3CH2CH2Cl with CCl2= CHCH2Cl, initiated by Fe(CO)5+DMF, the main addition products are respectively compounds of structure HCCl2CH(CCl2CH3)CH2CH2CHCl2 and HCCl2CH(CCl2CH2CHCl2)CH2C1. The formation of these compounds was explained by the isomeriza'tion of the radical-adducts CCl2CH(CCl2CH3)CH2CH2CH2Cl and CCl2CH(CCl2CH2CH2Cl)CH2Cl, with migration of a hydrogen atom from the CH2Cl groups found in the 5 position to the radical center.

The structure of chlorinated poly(vinyl chloride). VI. Comparison of the chlorination of poly(vinyl chloride) and β,β‐d2‐poly(vinyl chloride) with 1H‐NMR and 13C‐NMR spectroscopy

AbstractSamples of chlorinated poly(vinyl chloride) (CPVC) and chlorinated β,β‐dideuterated poly(vinyl chloride) (β,β‐d2‐CPVC) were prepared under identical reaction conditions. The microstructure of CPVC and β,β‐d2‐(CPVC) was characterized by a combination of 1H‐NMR, 13C‐NMR spectroscopy, and analytically determined chlorine content. A difference was observed in the reaction rates of chlorination of PVC and β,β‐d2‐PVC, and, in their thermal chlorination in solution, also in the structure of the chlorinated products. It was proved that in the chlorination of β,β‐d2‐PVC a new chlorine atom can also enter the originalCHCl group. The results are discussed from the standpoint of the chlorination mechanism.