Ion-dipole Complex Research Articles

Ion-dipole complex formation from deprotonated phenol fatty acid esters evidenced by using gas-phase labeling combined with tandem mass spectrometry

The behavior of para-hydroxy-benzyl and hydroxy-phenylethyl fatty acid esters and methoxy derivatives toward the NH 3/NH − 2 system was investigated. Under these negative ion chemical ionization (NICI) conditions, proton abstraction takes place mainly at the more acidic site (i.e., phenol); however, this reaction is not entirely regioselective. Using NICI-ND 3 conditions, both isomeric phenoxide and enolate molecular species are produced in competition from these phenol esters. Their respective low-energy collision-activated dissociation spectra are studied, and they strongly differ, showing that these molecular species are not convertible to a common structure. Analysis of specific fragmentations of the OD-enolate parent species labeled by ND 3 in the gas phase, indicates that by charge-promoted cleavage, isomerization into an ion—dipole intermediate takes place prior to dissociation. This complex, containing a ketene moiety, isomerizes into different isomeric forms via two consecutive proton transfers: the first, which is very exothermic, is irreversible in contrast to the second, less exothermic reaction, which occurs via a reversible process. It is evidenced by the loss of labeling at phenol or enolizable sites in the fragment ions. Such a stepwise process does not take place from the phenoxide parent ion, which preferentially yields a very stable carboxylate ion. A thermochemical approach, using estimated acidity values, yields a rationalization of the observed reactivities of the various substrates studied.

Ab initio molecular orbital study of 1-propanol(1+) ions

Several parent ion structures as well as dissociated product structures relevant to the dissociation of 1-propanol ions have been investigated by ab initio molecular orbital calculations. The species studied include the 1-propanol molecular ion, CH{sub 3}CH{sub 2}CH{sub 2}CH{sup +}, the distonic ion, CH{sub 2}CH{sub 2}CH{sub 2}OH{sub 2}{sup +}, the ion-dipole complex, c-C{sub 3}H{sub 6}{sup +}-H{sub 2}O, and a hydronium ion-allyl radical complex. In addition, the structures and energies of the transition states connecting these isomers and their dissociation products have been determined. The calculations were carried out with the GAUSSIAN 90 program using the 6-31G{sup *} and 6-31G{sup **} basis sets, the latter with inclusion of electron correlation by using Moller-Plesset perturbation theory truncated at second order. All bond lengths and angles were optimized and vibrational frequencies calculated. These calculations showed that the H loss channel and the rearrangement to the distonic ion are associated with substantial barriers. On the other hand, the distonic ion is separated from the ion-dipole complex by a relatively low barrier. The major finding is that the lower energy isomer of the propanol ion, in which the electron is removed from the {sigma} bond between the {alpha} and {Beta} carbons, lies 0.6 eV below themore » reported propanol ion heat of formation. The geometries, charge distributions, and vibrational frequencies are reported in this publication. An accompanying paper discusses the dissociation dynamics of propanol ions. 19 refs., 2 figs., 3 tabs.« less

Bimolecular reactions of the .beta.-distonic isomer of the ethanol radical cation: .bul.CH2CH2OH2+

Bimolecular reactions of {sup {sm_bullet}}CH{sub 2}CH{sub 2}OH{sub 2}{sup +} and its isomer, the ethanol radical cation, are studied by mass spectroscopy in this paper. The chemical properties of the distonic ion, which is described as a loosely-bound ion-dipole complex of ionized ethylene and water, do not reflect the ground-state structure and the observed reactivity is likely due to an electrostatically bound intermediate. 22 refs., 3 figs., 3 tabs.

Formation of the 3-pentanone ion from ionized propyl propanoate through ion-neutral complexes

Formation of the 3-pentanone ion ( 3) from ionized propyl propanoate through the complex [C 2H 5CO + .OC 3H 7] is proposed based on data obtained by photoionization. The threshold and energy dependence for forming 3 relative to those for related processes support this proposal. The threshold for forming 3 coincides with that predicted for forming [CH 3CH 2CO + .CH 2CH 3], suggesting that that complex is also an intermediate in the pathway to 3. 3-Pentanone ion formation is important much further above threshold than is alkane elimination through [RCO + .R] complexes. This adds to evidence that reactions between the partners in ion-dipole complexes take place over a wider energy range than do such reactions in complexes containing nonpolar neutral partners.

Primary and secondary kinetic isotope effects in the decomposition of a tertiary alkoxide

Kinetic isotope effects have been determined for the elimination of toluene from the alkoxide of 1,2,3-triphenylpropan-2-ol (1a). In DMSO, the rate measurements on 1a and [1,1,3,3-2H4] 1,2,3-triphenylpropanol (1b) at 30°C give kH4/kC4= 1.68. For the enolate products of reactions of [1,3-2H2]- and [1,1-2H2]-1,2,3-triphenylpropanol (1c and 1d), isolated as enol ethers, the ratio of deuteriated to undeuteriated products was 2.67 and 1.37, respectively. The ratio of undeuteriated to deuteriated toluenes from 1d was 1.46. In the reaction of [1-13C]-1,2,3-triphenylpropanol (1e) the ratio of 13C-labelled product to unlabelled was 1.064. The data are shown to be consistent with rate-limiting expulsion of a benzyl anion from the alkoxide, followed by fast proton transfers involving a solvent molecule to yield the observed products. The negative chemical ionization spectrum of 1a shows ions corresponding to deprotonated alcohol and the enolate of 1,2-diphenylethanone. The ratios of deuteriated to undeuteriated enolates in the B/E linked spectra of 1c and 1d were 2.47 and 0.72, respectively, and the ratio of 13C-enolate to unlabelled enolate in the fragmentation of 1e was 1.083. These data are rationalized in terms of an ionic fragmentation to an ion–dipole complex of 1,2-diphenylethanone and benzyl anion followed by a proton transfer which is at least partially rate limiting within the complex to yield the enolate.

The rates of HCl loss from energy-selected ethylchloride ions: A case of tunneling through an H-atom transfer barrier

The dissociation rates of energy-selected ethylchloride and deuterated ethylchloride ions were measured as a function of the parent-ion internal energy by the method of photoelectron photoion coincidence. Previously performed ab initio calculations indicated that the rate-determining step for this reaction is an H-atom transfer from the β carbon to the Cl atom via a substantial energy barrier of 92 kJ/mol (referenced to the zero-point energy). The ion internal energy range in which the experimental rates varied between 105 and 107 s−1 was found to lie well below the calculated barrier for H-atom transfer. The rates were modeled with the RRKM statistical theory which includes a tunneling step through an Eckart potential. The vibrational frequencies of both the normal and deuterated ethylchloride ions were determined by ab initio molecular-orbital methods. The theory accounted very well for the absolute rates including the strong deuterium isotope effect. The measured kinetic-energy release distribution appears nonstatistical. This indicates that the ion–dipole complex, which lies in between the transition state and the C2H+4+HCl products, is ineffective in randomizing the potential energy of the reverse activation barrier.

Transition structures for conjugate and carbonyl additions of cyanide to s-cis- and s-trans-acrolein. An ab initio MO study

Transition structures for the addition of cyanide anion to s-cis- and s-trans-acrolein and to ethylene and formaldehyde have been located with ab initio MO calculations with use of the 3-21 G and 6-31+G* basis sets. Energies of all stationary points, including reactants, ion-dipole complexes, and products, were evaluated at the second-order Moller-Plesset correlation level with the 6-31+G* basis set. The relative reaction barriers for conjugate and carbonyl additions are discussed for gas-phase and solution-phase reactions. Calculations predict that, in the gas phase, the reaction barrier for conjugate addition to s-cis-acrolein is slightly higher than that for carbonyl addition, wheareas the reverse situation is found for addition to s-trans-acrolein. The conjugate addition products are also more stable than the carbonyl addition products. The reaction barrier for carbonyl addition is expected to become smaller than that for conjugate addition in solution, under which conditions the difference in the stabilities of the conjugate and carbonyl products should become relatively small

The gas phase chemistry of the methyl carbamate radical cation H 2NCOOCH +3[rad]: isomerization into distonic ions, hydrogen-bridged radical cations and ion—dipole complexes

The unimolecular chemistry of the methyl carbamate radical cation, H 2NCOOCH + 3, 1, has been investigated by a combination of mass spectrometry based experiments (metastable ion (MI), collisional activation (CA), colision-induced dissociative ionization (CIDI), neutralization—reionization (NR) spectrometry, 2H, 13C and 18O isotopic labeling, appearance energy (AE) measurements), and ab initio molecular orbital calculations, executed at the SDCI/G—31G**//4—31G level of theory and corrected for zero-point energies. These calculations indicate that besides ionized methyl carbamate there are at least seven other equilibrium structures inlcuding distonic ions and hydrogen-bridged radical cations. The most stable isomer is the hydrogen-bridged species [H 2NCHO ⋯ H ⋯ OCH] + which is best viewed as the carbenium ion H 2NCHOH + interacting with the formly dipole. The related species [H 2NCO ⋯ H ⋯ OCH 2] + in which the hydroxyaminocarbene ion H 2NCOH + interacts with the formaldehyde dipole is also a stable species. This hydrogen-bridged radical cation is the key intermediate in the spontaneous unimolecular dissociations of methyl carbamate ions. Experimentally, the metastable molecular ions form two sets of products, namely. H 2NCHOH + + HCO (the components of the most stable isomer) and [CH 2O ⋯ H ⋯ NH 2] + + CO. The minimum energy requirement paths have been located by ab initio calculations and the reactions follow multistep isomerizations. In the first step, H 2NCOOCH + 3 , 1, isomerizes via a 1,4-hydrogen shift to the distonic ion H 2NC(OH)OCH + 2 , 2, which then rearranges to the hydrogen-bridged radical ion [H 2NCO ⋯ H ⋯ OCH 2] + . The incipient formaldehyde molecule can then donate a hydrogen to the C atom of H 2NCOH, followed by loss of HCO or it can accept the hydroxyl hydrogen to form a CH 2OH radical; this radical then migrates within the electrostatic field of the H 2 N + CO ion towards the N atom to form the complex [H 2CO ⋯ H ⋯ NH 2CO + . This latter species, which can be viewed as a formaldehyde and a CO molecule interacting with NH + 3 lies in a shallow potential well only and sheds CO to produce [CH 2O ⋯ H ⋯ NH 2] , as observed experimentally. It is stressed that only with the aid of high level ab initio calculations could the above mechanisms be elucidated.

ChemInform Abstract: Amine Selective Coloration with Chromoacerands

Amine selective complexation of some azophenol-dyed crowns with concurrent coloration and molecular structures of two sec. amine-dyed crown complexes are reported as well as selective colorations of enantiomeric amines with chiral azophenol crowns and of diamines with bisazophenol crown. INTRODUCTION A variety of complexes and inclusion compounds between tcationic or neutral guest and neutral host, e.g. crowns, cryptands, cyclodextrins, and antibiotics has been studied to develop the phase-transfer catalysis and to elucidate the mechanism of enzyme/substrate and naturally occurring ionophore /metal cation interactions so far. On the other hand, studies on complexation involving the coulombic attractive force between oppositely charged hosts and guests have been expected to draw a new trend in molecular recognition, since this additional binding force will affect the stability and selectivity of the complex other than ion-dipole interaction and/or hydrogen bonding. Previously we reported design and syntheses of a series of ligands which c selectively bind a given metal ion and undergo concurrently color ch gel e.g. lithium ion selective color tion with azophenol-dyed crowns?7 and azophenol spherand-like cyclophanefj, sion with benzothiazolylphenol crowns,'j and their application to lithium ion analyses. BP thium ion specific fluorescent emisAMINE SELECTIVE COMPLEXATION-COLORATION5 Now we wish to report selective complexation of protonated amines by the use of azophenol crowns 1-6 and podand 7 which have a phenol group in the cavity to yield the corresponding ammonium phenolate complex 1 0 (Scheme 1 ). The colored complex 1 0 must be differentiated from simple ion-dipole type complexes by an additional binding force, that is, coulombic interaction between the host phenolate anion and the guest ammonium cation. We recently observed such a perching type complexation of protonated amines by the phenolate anion and ether oxygens of the azophenol crowns.

A six-body potential energy surface for the SN2 reaction Cl-(g) + CH3Cl(g) and a variational transition-state-theory calculation of the rate constant

Correlated calculations (MP2/6-31G**) of the energies and frequencies at the saddle point, ion-dipole complex, and reactants plus additional energy calculations at selected geometries in the strong interaction region are used to parameterize a multidimensional potential energy function for the title reaction. Semiclassical variational transition-state theory is used to calculate the gas-phase rate coefficient and to determine a semiempirical value of the barrier height to reproduce the experimental value of this coefficient at 300 K. The semiempirical gas-phase barrier height is 3.1 kcal/mol. A new potential energy function with this barrier height is created and used to calculate the temperature-dependent rate coefficients and phenomenological activation energies for both CH{sub 3}Cl and CD{sub 3}Cl over the 200-1,000 K temperature range. The activation energy is predicted to show a large temperature dependence. The kinetic isotope effect is predicted to be 1.04 at room temperature.

Effect of nonequilibrium solvation on chemical reaction rates. Variational transition-state-theory studies of the microsolvated reaction Cl-(H2O)n + CH3Cl

The authors present a potential energy surface for the microhydrated S{sub N}2 reaction of a chloride ion with methyl chloride in the presence of one or two water molecules. All degrees of freedom are included. The authors analyze the stationary points corresponding to reactant, ion-dipole complex, and transition state for the monohydrated and the dihydrated reactions, and they use generalized transition-state theory to evaluate the rate constants for these reactions. A noteworthy feature of the dynamics calculations is that vibrational zero point effects are included, as are effects of quantization on vibrational heat capacities and entropies, and water molecules are treated as nonrigid. The authors find that the rate constant at 300 K decreases from the gas-phase value of 3.5 {times} 10{sup {minus}14} cm{sup 3} molecule {sup {minus}1} s{sup {minus}1} to a value of 1.1 {times} 10{sup {minus}17} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} for the monohydrated reaction and to a value of 3.7 {times} 10{sup {minus}20} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} for the dihydrated reaction.

A theoretical study of (N 2O) 2+, (CO 2) 2+ and N 2O +CO 2. Comparison of the two-center—three-electron bond and the ion—dipole complex

The binding energy of the (CO 2) 2 +, (N 2O) 2 + and N 2O +CO 2 complexes were calculated at the MP4/6-31G *//6-31G * and MP2/6-31+G * levels for two alternative structures. In one structure the positive charge is distributed evenly over both moieties, which leads to a two-center—three-electron (2c-3e) bonding interaction. In the other, one moiety carries the positive charge, which leads to an ion—dipole interaction. In the (CO 2) 2 + dimer the 2c-3e interaction is predicted to be 6 kcal mol −1 stronger than the ion—dipole interaction while in the (N 2O) 2 + dimer the 2c-3e interaction is 9 kcal mol −1 stronger. The binding energy of the (CO 2) 2 + dimer is in good agreement with experiment, but the binding energy of (N 2O) 2 + is overestimated by ≈6 kcal mol −1.

Tandem mass spectrometric investigation on 17β-estradiol palmitate in negative ion chemical ionization

In negative ion mass spectrometry (NI-MS) of bifunctional compounds (e.g. 17β-estradiol palmitate, containing two acidic sites), the orientation of the deprotonation process is greatly influenced by the (MH) − preparation mode [i.e. in solution for fast atom bombardment (FAB) and in the gas phase for chemical ionization (CI)]. Under negative ion FAB conditions, deprotonation is regioselective and takes place at position C 3 of a phenolic A ring whereas, in negative ion CI, competitive deprotonation occurs from both acidic sites of the molecule. Indeed, collisional activated dissociation (CAD) spectra of (MH) − present different fingerprints according to the preparation mode used. Using deuterium labelling in NI-FAB, no deuterium incorporation is observed on the deprotonated molecule [i.e. exclusive (M dD) − formation]. The situation is not the same as in NICI-ND 3 experiments since both (M dD) − and (M dH) − are produced in similar abundance. The observed differences in behavior of these (M dD) − and (M dH) − species towards high-energy collision (eV range, in triple quadrupole instrument) demonstrate that both ions were deprotonated from the C 3 A ring and from the enolizable position of the C 17 side chain, respectively. These CAD spectra provide evidence that these deprotonated forms are not convertible. Furthermore, the diagnostic daughter ions produced under CAD conditions indicate that, prior to collision, two different ion-dipole complexes are formed from the precursor (M dD) − and (M dH) − ions.

Amine selective coloration with chromoacerands

Abstract

The ClHCl− anion: Its chemical bond, vibrations, and free energy

The geometry of ClHCl− has D∞h symmetry, [Cl–H–Cl]−, as opposed to C∞v symmetry [Cl–H...Cl−], which is predicted to be favored at the Hartree–Fock (HF) level of calculation with a basis set of [11s9p2d1f(Cl)/5s2p1d(H)]. The chemical bond of the D∞h structure is a nonclassical four-electron three-center bond, while the C∞v geometry corresponds to an ion–dipole complex. The energy difference between the two is small. Calculations with inclusion of configuration revealed that both have predominantly a HF configuration. D∞h is realized by excitations from σ molecular orbitals (MO) to their antibonding σ* MO, whereas excitations to π MO are ineffective. Normal vibrational frequencies were calculated as follows (units are cm−1): G82(MP2): (ν1,σg): 346; (ν3,σu ): 547; (ν2,πu): 854; 1D Analysis(MP4): (ν1,σg ): 338; (ν3,σu): 830; (ν2, πu ):...; 2D Analysis(MP4): (ν1,σg): 310; (ν3,σu) : 709; (ν2,πu) : 877. The potential for the asymmetric vibration is shown to be quartic. The standard free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes (i.e., at 1 atm and 298.16 K) were evaluated from the reaction, HCl+Cl−→ClHCl−, to be as follows: ΔG°=−16.5 kcal/mol, ΔH°=−23.5 kcal/mol, and ΔS°=−23.5 cal/K/mol.

Reactions of isolated organic ions. Alkene loss from the immonium ions CH3CHN+HC2H5and CH3CHN+HC3H7

The slow unimolecular reactions of metastable CH3CHN+HR [R = C2H5, (CH3)2CH, and CH3CH2CH2] ions are reported and discussed in energetic and mechanistic terms. These immonium ions eliminate an alkene (R–H) derived by hydride abstraction from the incipient carbonium ion R+. This reaction is interpreted as occurring via an ion–dipole complex comprising the incipient carbonium ion co-ordinated to CH3CHNH, followed by rearrangement to another complex in which (R–H) and CH3CHNH are bound to a common proton. 2H-Labelling experiments show a different specificity in the hydrogenabstraction step for R = ethyl and R =n-propyl: transfer of a deuterium atom from the β-carbon predominates when R = CH2CD3, but CH3CHN+HCD2CH2CH3 expels a substantial proportion of C3H5D. The behaviour of the CH3CHN+HR ions is compared with that of their CH2N+HR homologues. An analysis is presented of the influence of the structure of R on the properties of the associated ion-dipole complexes.

Fragmentation of alkoxide ions following collisional activation. An energy-resolved study

The collisionally activated dissociation reactions of the C2 to C5 alkoxide ions have been studied for collisons occurring at 8 keV kinetic energy and also over the range 5 to 100 eV kinetic energy. The alkoxide ions fragment by 1,2-elimination of H2 and/or an alkane. Thus, primary alkoxide ions fragment by elimination of H2 only, secondary alkoxide ions show elimination of H2 and alkane molecules, while tertiary alkoxide ions show elimination of alkanes only. In alkane elimination, loss of CH4 is much more facilie than loss of larger alkanes. For secondary alkoxide ions, where more than one elimination reaction occurs, the energy dependence of fragmentation has been explored over the collision energy range 5 to 100 eV. The results are interpreted in terms of a step-wise mechanism involving formation of an anion-carbonyl compound ion-dipole complex, followed by proton abstraction by the H− or alkyl anion leading to the final products. The relative importance of the reaction channels is determined by the relative stabilities of these ion-dipole complexes.

ChemInform Abstract: Ion‐Dipole Complexes in the Unimolecular Reactions of Isolated Organic Ions. Effect of N‐Methylation on Olefin and Amine Loss from Protonated Aliphatic Amines.

ChemInformVolume 19, Issue 40 Preparative Organic Chemistry ChemInform Abstract: Ion-Dipole Complexes in the Unimolecular Reactions of Isolated Organic Ions. Effect of N-Methylation on Olefin and Amine Loss from Protonated Aliphatic Amines. R. D. BOWEN, R. D. BOWEN Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this authorA. G. HARRISON, A. G. HARRISON Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this authorE. J. REINER, E. J. REINER Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this author R. D. BOWEN, R. D. BOWEN Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this authorA. G. HARRISON, A. G. HARRISON Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this authorE. J. REINER, E. J. REINER Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this author First published: October 4, 1988 https://doi.org/10.1002/chin.198840100Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue40October 4, 1988 RelatedInformation

Ion–dipole complexes in the unimolecular reactions of isolated organic ions. Fragmentation of protonated and cationated formate and acetate esters

The unimolecular fragmentation reactions occurring on the metastable ion time scale have been determined for protonated alkyl formates and acetates and for the adducts of CD3+ and C2H5+ with these esters. The protonated esters, R1CO2RH+, fragment to form R+ + R1CO2H or, by internal hydrogen transfer, R1CO2H2+ + (R – H) with the relative yields depending on the identity of R1 and R. Using deuterium labelling it has been shown that the added proton interchanges with hydrogens of the R group prior to fragmentation. The methyl-d3-cationated esters, R1CO2R•CD3+, mostly fragment to give R1CO2CD3, H+ by elimination of (R – H), although R+ formation is observed in a few cases. The ethyl-cationated esters fragment primarily to give R1CO2C2H5•H+ by elimination of (R–H); specifically no elimination of C2H4 is observed. All of the results can be rationalized in terms of a step-wise mechanism of fragmentation involving initial formation of an ion–dipole complex of the alkyl ion R+ with a carbonyl compound. This complex may either fragment to form R+ or may proceed by way of an ion–dipole complex of a protonated carbonyl and an olefin to the protonated species plus (R – H). The results indicate that primary alkyl ions are not formed but rather that rearrangement to the more stable secondary or tertiary structure occurs. There is some evidence that s-butyl cations are not formed, but that these too rearrange to the t-butyl structure.

The [CH2 = CHOH/H2O]+˙ system: A theoretical study of distonic ions, hydrogen‐bridged ions and ion–dipole complexes

AbstractSeveral isomeric forms of the vinyl alcohol/water radical cation have been investigated by high‐level ab initio molecular orbital theory calculations, including electron correlation effects. Of the ions considered here, the anti form of the O ⃛H ⃛O bridged complex is calculated to be the lowest in energy, having a stabilization energy of 100 kJ mol−1 with respect to the dissociation products [CH2CHOH]+˙ and H2O. Although the isomeric ions may formally be represented as distonic ions, hydrogen‐bridged ions and ion–dipole complexes, the only significant barrier separating the isomers appears to be the anti↔syn isomerization barrier. However, in the O ⃛H ⃛O bridged complex this barrier is found to be considerably lowered relative to the anti↔syn isomerization barrier for the free vinyl alcohol radical cation.