Reaction of [HO(CH2)3]3P with α,β-Unsaturated Ketones Containing a Phenylpropanoid Backbone

Abstract

Interaction of 3,4-(MeO)₂-benzylideneacetone with [HO(CH₂)₃]₃P (THPP) was studied in CD₃OD by NMR to compare reactivity of a phenylpropanoid α,β-unsaturated ketone with a corresponding α,β-unsaturated aldehyde. In the presence of HCl, both the ketone and a related cinnamaldehyde first establish an equilibrium with the product formed by nucleophilic attack of the THPP at the C?O bond, [ArCH?CHCX(OD)PR₃]⁺Cl^?(X?H or CH₃, Ar?Ph or 3,4-(MeO)₂C₆H₃). The ketone salt then slowly transforms into [R₃PCH(Ar)CH(D)C(O)CD₃]⁺Cl^?, the phosphonium product of nucleophilic attack of THPP at the C?C bond, whereas the final product from the aldehyde is the (α-ether)phosphonium chloride [ArCH?CHCH(OCD₃)PR₃]⁺Cl^?. In aqueous media, in the absence of HCl, 4-HO-benzylideneacetone, which is similar to a lignin-type, α,β-unsaturated aldehyde model compound, interacts with THPP to afford a stable phosphonium zwitterion, in contrast to the previously studied aldehyde model, which forms dimeric, bisphosphonium products.     

CH2 + transfer to pyridine nucleophiles: a means of producing α-distonic ions

The distonic radical cation C₅H₅N⁺?^·CH₂ can be generated by the reactions of neutral pyridine with the radical cations of cyclopropane, ethylene oxide, and ketene, as well as with the [C₃H₆]⁺ ion from fragmentation of tetrahydrofuran. The distonic product ion can be distinguished from isomeric methylpyridine radical cations because the former gives characteristic [M?CH₂]⁺, [M ? CH₂NCH]⁺, and a doubly charged ion, all of which are produced on collisional activation. Furthermore, the distonic species completely transfers CH₂ ⁺ to more nucleophilic, substituted pyridines. These properties are all consistent with the assigned distonic structure. Another distonic isomer, the (3-methylene) pyridinium ion, can be distinguished from the (1-methylene)pyridinium ion on the basis of their different fragmentation behaviors. The latter ion exhibits higher stability (lower reactivity) than the prototypal [·CH₂NH₃ ⁺], making available a distonic species whose bimolecular reactivity can be readily investigated.     

Chemical ionization of cyclopropyl ethers II—the nature of the alkyl group fragmentationt

Oxygen-alkyl cleavage is ruled out in the methane chemical ionization- and electron mpact-induced decomposition of cyclopropyl ethers by the finding that for trans,trans-2,3-diethylmethoxycyclopropane the [M ? C₂H₅·]+ ion is more intense than the [M ? CH₃·]+ ion. The possibility for [M + H ? C₂H₆]⁺ is discounted by comparison with the methane chemical ionization nass spectrum of tran,tran-2,3-dimethylmethoxycyclopropane. The isobutane chemical ionization nass spectrum of the diethylcyclopropyl methyl ether affords nearly exclusive electrocyclic methanol fragmentation, i.e. [M + H ? CH₃OH]⁺.     

The significance of field ionisation kinetics to ion structure: Isomerisation and decompostition of [C4H8]+· radical ions

The kinetics of formation of [C₃H₅]⁺[M ? CH₃]⁺, [C₃H₄]⁺·[M ? CH₄]⁺· and [C₂H₄]⁺·[M ? C₂H₄]⁺· from but-1-ene, cis- and trans-but-2-ene, 2-methylpropene, cyclobutane and methylcyclopropance following field ionisation have been determined as a function of time 20 (or 30) picoseconds to 1 nanosecond and at two points in the microsecond time-frame. The results are consistent with the supposition that at the shortest accessible times (20 to 30 picoseconds) the structure of the [C₄H₈]⁺· molecular ion qualitatively resembles that of its neutral precursor, but suggest that prior to decomposition within nanoseconds the various molecular ions (excepting cyclobutane where the processes are slower) attain a common structure or mixture of structures. Reaction pathways of the presumed known ion structures are delineated from the nature of decompostion at the shortest times.     

Loss of methyl from [H2CC(OH)?CH3]+˙ ions prepared by electron impact ionization of unstable 2-hydroxypropene

Unstable 2-hydroxpropene was prepared by retro-Diels-Alder decomposition of 5-exo-methyl-5-norbornenol at 800°C/2 × 10^?6 Torr. The ionization energy of 2-hydroxypropene was measured as 8.67±0.05 eV. Formation of [C₂H₃O]⁺ and [CH₃]⁺ ions originating from different parts of the parent ion was examined by means of ¹³C and deuterium labelling. Threshold-energy [H₂C?C(OH)? CH₃]^+˙ ions decompose to CH₃CO⁺+CH₃^˙ with appearance energy AE(CH₃CO⁺) = 11.03 ± 0.03 eV. Higher energy ions also form CH₂?C?OH⁺ + CH₃ with appearance energy AE(CH₂?C?OH⁺) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C₂H₃O]⁺ ions containing the original methyl group and [CH₃]⁺ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate-determining isomerization [H₂C?C(OH)? CH₃]^+˙ →[CH₃COCH₃]^+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.     

A mass spectral study of 1-(aryldimethylsilyl)-2-propanones and their isomeric 2-(aryldimethylsiloxy)-1-propenes

The mass spectra of a series of β-ketosilanes, p-Y? C₆H₄Me₂SiCH₂C(O)Me and their isomeric silyl enol ethers, p-Y? C₆H₄Me₂SiOC(CH₃)?CH₂, where Y = H, Me, MeO, Cl, F and CF₃, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]⁺, [M? C₆H₄Y·]⁺, [M? Me₂SiO]⁺˙, [M? C₃H₄]⁺˙, [M? HC?CCF₃]⁺˙, [Me₂SiOH]⁺˙ and [C₃H₆O]⁺˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me₂SiO]⁺˙ and [Me₂SiOH]⁺˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.     

Doubly charged benzene and isomeric dications. Fragmentation energetics and charge distributions calculated by MINDO/3 molecular orbital theory

MINDO/3 calculations for singlet and triplet doubly charged benzene [C₆H₆]²⁺ are in satisfactory agreement with the experimentally determined values of the vertical double ionization energy of benzene; calculations for straight chain isomeric structures are consistent with the observed kinetic energy release on fragmentation to [C₅H₃]⁺ and [CH₃]⁺. Symmetrical doubly charged benzene ions relax to a less symmetrical cyclic structure having sufficient internal energy to fragment by ring opening and hydrogen transfer towards the ends of the carbon chain. Fragmentation of [CH₃C₄CH₃]²⁺ to [CH₃C₄]⁺ and [CH₃]⁺ is a relatively high energy process (A), whereas both (B): [CH₃CHC₃CH₂]²⁺ to [CHC₃CH₂]⁺ and [CH₃]⁺ and (C): [CH₃CHCCHCCH]²⁺ to [CHCCHCCH]⁺ and [CH₃]⁺ may be exothermic processes from doubly charged benzene. Furthermore, the calculated energy for the reverse of process (A) is less than the experimentally observed kinetic energy released, whereas larger energies for the reverse of processes B and C are predicted. Heats of formation of homologous series [HC_n]⁺, [CH₃C_n]⁺, [CH₂C_n?2CH]⁺, [CH₃C_n?2CH₂]⁺ and [CH₂?CHC_n?3CH₂]⁺ with 1 < n < 6 are calculated to aid prediction of the most stable products of fragmentation of doubly charged cations. The homologous series [CH₂C_n?2CH]⁺ is relatively stable and may account for ready fragmentation of doubly charged ions to [C_nH₃]⁺; alternatively the symmetrical [C₅H₃]⁺ ion [CHCCHCCH]⁺ may be formed. Dicoordinate carbon chains appear to be important stabilizing features for both cations and dications.     

Structure and formation of gaseous [C4H6O]+˙ ions: 1—The enolic ions [CH2C(OH)?CHCH2]+˙ and [CH2CH?CHCH(OH)]+˙ and their relationship with their keto counterparts

The [C₄H₆O]^+˙ ion of structure [CH₂?CHCH?CHOH]^+˙ (a) is generated by loss of C₄H₈ from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔH_f of [CH₂?CHCH?CHOH]^+˙ was estimated to be 736 kJ mol^?1. The isomeric ion [CH₂?C(OH)CH?CH₂]^+˙ (b) was shown to have ΔH_f, ? 761 kJ mol^?1, 54 kJ mol^?1 less than that of its keto analogue [CH₃COCH?CH₂]^+˙. Ion [CH₂?C(OH)CH?CH₂]^+˙ may be generated by loss of C₂H₄ from ionized hex-1-en-3-one or by loss of C₄H₈ from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C₄H₆O]^+˙ ion generated by loss of C₂H₄ from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH₂?CHCH?CHOH]^+˙ and [CH₂?C(OH)CH?CH₂]^+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH₃˙ and CO, [CH₂?CHCH?CHOH]⁺˙ and [CH₂?C(OH)CH?CH₂]^+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C₄H₆O]^+˙ ion [CH₂?C?CHCH₂OH]^+˙ are also reported.     

Four-centred rearrangements in the mass spectra of aliphatic ethers

The [CH₃O?CHCH₃]⁺ ions observed in the mass spectra of ethers of formula CH₃OCH (CH₃)R(R = H or alkyl) undergo two rearrangement fragmentation reactions to form [C₂H₅]⁺ and [CH₂OH]⁺. The scope of the rearrangements has been investigated and it is shown that enlargement of the alkyl group on either side of the ether linkage leads to alternative fragmentation routes. From a study of metastable intensities it is concluded that the fragmentations probably occur directly from the [CH₃O?CHCH₃]⁺ structure through four centred rearrangements rather than through the intermediacy of the [C₂H₅O?CH₂]⁺ ion.     

An energy-resolved study of the fragmentation of ionized 1-Penten-3-ol

A detailed energy-resolved study of the fragmentation of CH₂?CHCH(OH)CD₂CD₃ (1-d₅) has been carried out using metastable ion studies and charge exchange techniques, combined with collision-induced dissociation studies to establish the structures of fragment ions. At low internal energies (metastable ions) the molecular ion of 1-d₅ rearranges to the 3-pentanone structure and fragments by loss of C₂H₅ or C₂D₅ leading to the acyl structure, [CH₃CH₂C?O]⁺ or [CD₃CD₂C?O]⁺, for the fragment ion. However, with increasing internal energy of the molecular ion this rearrangement process decreases rapidly in importance and loss of C₂D₅ by direct cleavage, leading to [CH₂?CHCH?OH]⁺, becomes the dominant fragmentation reaction. As a result the [C₃H₅O]⁺ ion seen in the electron impact mass spectrum of 1-penten-3-ol has predominantly the protonated acrolein structure.     

The structure and mechanism of formation of C5H9O+ from ionized phytyl methyl ether

The recent proposal that ionized phytyl methyl ether [C₁₆H₃₃(CH₃)C=CHCH₂OCH ₃ ^+· ] undergoes an allylic rearrangement to ionized isophytyl methyl ether [CH₂=CHC(C₁₆H₃₃)(CH₃)OCH ₃ ^+· ] before elimination of an alkyl radical is discussed. Both literature precedent and new results in which the structure of the [M-C₁₆H ₃₃ ^· ]⁺ fragment ion is established by comparison of its collision-induced dissociation mass spectrum with the spectra of isomeric C₅H₉O⁺ ions of known structure are inconsistent with this proposal. The forma Hon of CH₃CH=CHCH=O⁺CH₃ by loss of a γ-alkyl substituent without skeletal isomerization rather than CH₂=CHC(CH₃)=O⁺CH₃ after allylic rearrangement is explained in terms of a mechanism that involves two 1,2-H shifts, followed by σ-cleavage of the resultant ionized enol ether, C₁₆H₃₃(CH₃)CH-CH=CHOCH ₃ ^+· .     

Skeletal and hydrogen rearrangements in the electron impact mass spectrum of propene

The mass spectrum of propene-2-[¹³C] shows 81% retention of C-2 in the [C₂H₃]⁺ fragment ion at 70 eV electron energy, decreasing to 75% C-2 retention at low electron energies. The mass spectra of propene-2-d₁, propene-1,1,3,3,3-d₅, propene-1,1,2-d₃ and propene-3,3,3-d₃ also have been examined at a resolution sufficient to resolve H₂-D doublets. The results at 70 eV electron energy show complete H/D randomization prior to fragmentation to form [C₃(H, D)₅]⁺ but, in agreement with the ¹³C labelling data, incomplete H/D interchange prior to fragmentation to form [C₂(H, D)₃]⁺. The results are interpreted in terms of a reversible isomerization of the propene molecular ion to a cyclopropane structure in competition with fragmentation.     

Structure and fragmentations of [C3H7S]+ ions

The principal fragmentation reactions of metastable [C₃H₇S]⁺ ions are loss of H₂S and C₂H₄. These reactions and the preceding isomerizations of [C₃H₇S]⁺ ions with six different initial structures were studied by means of labelling with ¹³C or D. From the results it is concluded that the loss of H₂S and C₂H₄ both occur at least mainly from ions with the structure [CH₃CH₂CH? SH]⁺ or from ions with the same carbon sulfur skeleton, with the exception of the ions with the initial structure [CH₃CH₂S? CH₂]⁺, which partly lose C₂H₄ without a preceding isomerization. For all ions, more than one reaction route leads to [CH₃CH₂CH?SH]⁺. It is concluded that the loss of H₂S is at least mainly a 1,3-elimination from the [CH₃CH₂CH?SH]⁺ ions. Both decomposition reactions are preceded by extensive but incomplete hydrogen exchange.     

The mass spectral fragmentation of phenyl ω-dialkoxyethyl tellurides

The 70 eV mass spectrum of phenyl ω-dimethoxyethyl telluride [C₆H₅? Te? CH₂CH(OR)₂, R?CH₃]contains an intense peak at m/z 238 which corresponds to a rearrangement ion [C₆H₅? Te? OR]⁺. The formation of this species is further illustrated by the presence of a peak at m/z 241 in the spectrum of the hexadeuterated analog (R?CD₃) and a peak at m/z 252 in the spectrum of the ethyl analog (R?CH₂CH₃). These combined results illustrate the presence of only one of the alkoxyl groups in the rearrangement ion. Several other abundant ions that contain oxygen but not tellurium are present in the spectra of these compounds. High resolution analyses have aided in the determination of the origin and composition of several of the characteristic ions formed upon electron impact fragmentation of phenyl ω-dimethoxyethyl telluride.     

Luminescence in near-thermal charge exchange. III. CH(+) and CD(+) A → X emission from He+ C2H2 and He+ + C2D2

A pulsed ICR cell fitted with synchronous photon counting equipment is used to investigate the emission produced between 185 and 500 nm by near-thermal charge exchange between He⁺ and C₂H₂ (C₂D₂). The emission bands observed are A ²Δ → X²π and (weakly) B²Σ^? → X²π in CH(CD) and A ¹π → X¹Σ in CH⁺(CD⁺). Wavelength measurements on the bandheads of the (0,0) and (0,1) bands of CD⁺ A → X are used to evaluate vibrational constants of CH⁺(CD⁺) X¹Σ⁺. The results are (in cm^?1): ω_e = 2869 ± 27 (2106 ± 20); ω_eχ_e = 65 ± 13 (35 ± 7). These constants are used to calculate Morse-potential Franck—Condon factors and vibrational branching ratios for CH⁺ and CD⁺ A → X emission. The spectral distributions and the (relatively low) absolute emission rates produced by He⁺/C₂H₂(C₂D₂) charge exchange are briefly discussed in the light of presently available information on the charge transfer reaction and on the excited states of C₂H_2?⁺     

Mass spectrometric investigation of stereosomeric 1,2-dimethyl-4-substituted decahydroquinol-4-ol N-oxides. Concerning the configuration of the asymmetric nitrogen atom

The main fragmentation pathways of the N-1, C-2 and C-4 stereoisomers of the 1,2-dimethyl-4-R-transdecahydroquinoline-4-ol N-oxides (R=C?CH, CH?CH₂ and C₂H₅) under electron impact are discussed. The correlation between the mass spectrometric chromatographic behaviour and the configuration of polar groups in the N-oxides examined is discussed. The mass spectra of the N-1 stereoisomers may be subdivided into two groups, depending only on the orientation of N→O group and not of the 4-OH group. The spectra of N-oxides with the axial N-oxide group reveal less intense ions and much more intense [M? CH₃]⁺, [M? O]⁺, [M? OH]⁺ and ions, whereas in the spectra of their equatorial epimers the abundance of the ions exceeds the intensities of the latter ions.     

Ethene loss kinetics of methyl 2-methyl butanoate ions studied by threshold photoelectron-photoion coincidence: The enol ion of methyl propionate heat of formation

Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been used to investigate the unimolecular chemistry of gas-phase methyl 2-methyl butanoate ions [CH₃CH₂CH(CH₃)COOCH₃^·+]. This ester ion isomerizes to a lower energy distonic ion [CH₂CH₂CH(CH₃)COHOCH₃^·+] prior to dissociating by the loss of C₂H₄. The asymmetric time of flight distributions, which arise from the slow rate of dissociation at low ion energies, provide information about the ion dissociation rates. By modeling these rates with assumed k(E) functions, the thermal energy distribution for room temperature sample, and the analyzer function for threshold electrons, it was possible to extract the dissociative photoionization threshold for methyl 2-methyl butanoate which at 0 K is 9.80 ± 0.01 eV as well as the dissociation barrier of the distonic ion of 0.86 ± 0.01 eV. By combining these with an estimated heat of formation of methyl 2-methyl butanoate, we derive a 0 K heat of formation of the distonic ion CH₂CH₂CH(CH₃)COHOCH₃^·+ of 101.0 ± 2.0 kcal/mol. The product ion is the enol of methyl propionate, CH₃CHCOHOCH₃^·+, which has a derived heat of formation at 0 K of 106.0 ± 2.0 kcal/mol.     

Reaction of photogenerated fluorine atoms with dopant molecules in solid argon

The products of reactions of dopant CH₄ molecules with F atoms diffusing in solid argon at 20–30 K were identified by ESR and FTIR spectroscopy. The F atoms stabilized in the matrix were generated by UV photolysis of Ar?CH₄(CD₄)?F (1000∶1∶1) samples at 13 K. Subsequent heating above 20 K results in thawing off diffusion of the F atoms and formation of products of their reaction with CH₄: radical-molecular complexes^·CH₃?HF (^·CD₃?DF) and radicals^·CH₃ (^·CD₃). The ESR spectra of the radicala are similar to those observed for matrix-isolated^·CH₃. The^·CH₃?HF complexes are characterized by the IR band of HF stetching vibration at 3764 cm^?1. Two additional splittings on the H (a _H·=2 G) and F(a _F=16G) nuclei of the HF molecule appeal in the ESR spectrum of the complex. The latter splitting is retained in the^·CD₃?DF complex, whereA _D· <0.3G The rate constant of the reaction CH₄+F→^·CH₃+HF is equal to ?10^?25 cm³s^?1 at 20 K. Its activation energy (1.7±0.2 kcal mol^?1) is ?0.5 kcal mol^?1 greater than that in the gas phase. The collinear C_3v-configuration of the^·CH₃?HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by the comparison of the exprrimental constants of hyperfine coupling with the results of the quantum-chemical calculation.     

Synthesis and Surface Properties of Novel Cationic Gemini Surfactants

A series of novel cationic gemini surfactants, p-[C _n H_2n+1N⁺(CH₃)₂CH₂CH(OH)CH₂O]₂C₆H₄·2Cl^? [A(n = 12), B(n = 14) and C(n = 16)], containing a spacer group with two flexible and hydrophilic groups (2-hydroxy-1,3-propylene) on both sides of a rigid and hydrophobic group (1,4-dioxyphenylene) has been synthesized by the reaction of hydroquinone diglycidyl ether with N,N-dimethylalkylamine and N,N-dimethylalkylamine hydrochloride. Their surface-active properties have been investigated by surface tension measurement. The critical micelle concentration (cmc) values of the synthesized cationic gemini surfactants are one order of magnitude lower than those of their corresponding monomeric surfactants (C _n H_2n + 1N⁺(CH₃)₃·Cl^?). Both the cmc and surface tension at the cmc (γ_cmc) of A are lower than those of p-[C₁₂H₂₅N⁺(CH₃)₂CH₂]₂C₆H₄·2Cl^? (D). The novel cationic gemini surfactants A and B also show good foaming properties.     

A comparative study on the behaviour of 1,3-diheterocyclopentanes (X = O,O; S,S; O,S) under electron impact. The formation of thioacetyl and thiiranyl cations

The electron-impact-induced mass spectra of 1,3-dioxolane (la), 1,3-dithiolane (2a) and 1,3-oxatbiolane (3a) and their 2-methyl (1b–3b) and 2,2-dimethyl [(CH₃)₂: 1c–3c or (CD₃)₂: 1d–3d] derivatives have been studied in detail to gain further insight into their ion structures and competing reaction pathways with low-resolution, high-resolution, metastable and collision-induced dissociation (CID) techniques. For compounds 1a–1d the most significant reaction is loss of H^˙ and CH₃^˙ by α-cleavage and a subsequent formation of CHO⁺ and C₂H₃O⁺ ions. The [M ? H]⁺ ions from 1a and 1b give a C₂H₃O⁺ ion which does not have the acyl cation structure as shown by their CID spectra. In compounds 3a–3d the sulphur-containing ions predominate, the C₂H₃O⁺ now having the acyl cation structure. 1,3-Dithiolanes (2a–2d) exhibit the most complicated fragmentation patterns. Furthermore the [M ? H]⁺ ion from 2a and [M ? CH₃]⁺ ion from 2b have different structures as well as the [M ? H]⁺ ion from 2b and [M ? CH₃]⁺ ion from 2c, as shown by their CID spectra. This can be utilized to explain why 3a–3c and 2a give principally a thiiranyl cation, whereas 2b gives a mixture of this and the thioacyl cation and 2c practically only the open-chain thioacetyl cation.