Sequential Bond Dissociation Energies Research Articles

Electrostatic, sequential bond energies and structures of Li+·(N2)n complexes: computational study

The MP2 and CCSD calculations of the geometries and binding energies of the Li+·(N2)n (n = 1–4) complexes are obtained. The potential energy surface showed that these complexes exhibit one minimum state and one transition state. The mono- and di-ligated complexes exhibit linear configurations with a binding energy of 11.1 and 21.2 kcal mol−1, respectively. Trigonal planar and tetrahedral configurations are obtained for tri- and tetra-ligated complexes, respectively. The computed sequential bond dissociation energies (BDEs) of Li+·(N2)n (n = 1–4) complexes are also calculated in which the mono-ligated complex has the largest BDE value. The obtained trend is mainly dependent on the variation in the ion-quadrupole interaction of these ion complexes. These calculations predict that these complexes are of purely electrostatic nature.

Interaction energies and structures of the $$\hbox {Li}^{+}{\cdot }(\hbox {CO})_{\hbox {n}}$$ Li + · ( CO ) n (n $$=$$ = 1–3) complexes

The bonding and structures of lithium ion carbonyl complexes, $$\hbox {Li}^{+}{\cdot }$$ (CO) $$_{1-3}$$ , were studied at the CCSD and MP2 levels of theories. A linear configuration is formed for the global minimum of the $$\hbox {Li}^{+}{\cdot }$$ CO and $$\hbox {Li}^{+}{\cdot }(\hbox {CO})_{2}$$ complexes with bond dissociation energies of 13.7 and 12.4 kcal $$\hbox {mol}^{-1}$$ , respectively. For the $$\hbox {Li}^{+}{\cdot }(\hbox {CO})_{3}$$ complex, a trigonal planar geometry is formed for the global minimum with a bond dissociation energy of 9.7 kcal $$\hbox {mol}^{-1}$$ . The computed sequential bond dissociation energies of $$\hbox {Li}^{+}{\cdot }(\hbox {CO})_{\mathrm{n}}$$ (n $$=$$ 1–3) complexes agreed with the experimental findings, in which the electrostatic energy plays an important role in the obtained trend. Lithium ion binds with carbon oxides and form three complexes of linear and trigonal planar geometries. These structures affect their sequential bond dissociation energies based on the strength of electrostatic energy contributions. These results match the experimental findings.

Hydrated copper ion chemistry: guided ion beam and computational investigation of Cu2+(H2O)n (n = 7-10) complexes.

Cross sections for the threshold collision-induced dissociation of Cu(2+)(H(2)O)(n), where n = 8 - 10, are measured using a guided ion beam tandem mass spectrometer. The primary dissociation pathway is found to be loss of a single water molecule followed by the sequential loss of additional water molecules until n = 8, at which point charge separation to form CuOH(+)(H(2)O)(4) (+) H(+)(H(2)O)(3) is observed to occur at a slightly lower energy than loss of a water molecule. Competition from charge separation prohibits the formation of appreciable amounts of the n = 7 or smaller complexes as reactants in the source. These findings indicate that Cu(2+) has a critical size of 8. Analysis of the data using statistical modeling techniques that account for energy distributions and lifetime effects yields primary and sequential bond dissociation energies (BDEs) for loss of one and two water molecules from n = 8 - 10 complexes as well as the barrier for charge separation from n = 8. More speculative analysis extends the thermochemistry obtained down to n = 5 and 6. Theoretical BDEs are determined from quantum chemical calculations using structures optimized at the B3LYP/6 311(+)G(d,p) level along with the lowest-energy isomers suggested by single point energies at the MP2(full), M06, B3LYP, and B3P86 levels of theory using a 6- 311(+)G(2d,2p) basis set. BDEs at 0K are converted to 298 K thermodynamic values using a rigid rotor/harmonic oscillator approximation. Experimental and theoretical entropies of activation suggest that a third solvent shell forms at n = 9, in accord with previous findings. The present work represents the first experimentally determined hydration enthalpies for the Cu(2+)(H(2)O)n system.

Hydration Enthalpies of Ba(2+)(H2O)x, x = 1-8: A Threshold Collision-Induced Dissociation and Computational Investigation.

The sequential bond dissociation energies (BDEs) of Ba(2+)(H2O)x complexes, where x = 1-8, are determined using threshold collision-induced dissociation (TCID) in a guided ion beam tandem mass spectrometer. The electrospray ionization source generates complexes ranging in size from x = 6 to x = 8 with smaller complexes, x = 1-5, formed by an in-source fragmentation technique. The only products observed result from sequential loss of water ligands. Charge separation, a process in which both hydrated singly charged barium hydroxide and hydronium ion are formed, was not observed except for Ba(2+)(H2O)3 yielding BaOH(+) + H5O2(+). Modeling of the kinetic energy-dependent cross sections, taking into account the number of collisions, energy distributions, and lifetime effects for both primary and secondary water loss, provides 0 K BDEs. Experimental thermochemistry for the x = 1-3 complexes is obtained here for the first time. Hydration enthalpies and reaction coordinate pathways for charge separation are also examined computationally at several levels of theory. Our experimental and computational work are in excellent agreement in the x = 1-6 range. The present experimental values and theoretical calculations are also in reasonable agreement with the available literature values for experiment, x = 4-8, and theory, x = 1-6. Of the numerous calculations performed in the current study, B3LYP/DHF/def2-TZVPP calculations including counterpoise corrections reproduce our experimental values the best, although MP2(full)/DHF/def2-TZVPP//B3LYP/DHF/def2-TZVPP results are comparable.

Sequential bond energies and structures of the Cr + ⋅(N 2 ) n , n =1 −4

DFT calculations, with an effective core potential for the chromium ion and large polarized basis set functions have been used to calculate the sequential bond dissociation energies of the Cr+⋅(N2)n (n = 1—4) complexes. A linear configuration was obtained for the Cr\(^{+}\cdot \textit {N}_{2}\) and Cr+⋅(N2)2 complexes with sequential bond dissociation energies of 14.6 and 16.4 kcal mol−1, respectively. For the Cr+⋅(N2)3 and Cr+⋅(N2)4 complexes, distorted trigonal pyramidal and tetrahedral geometries were optimized with sequential bond dissociation energies of 6.5 and 5.5 kcal mol−1, respectively. π- back-donation in side-on approach of the Cr\(^{+}\cdot \textit {N}_{2}\) leads to the formation of a tilted structure with the Cr+ ion in central position. The di-ligated complex exhibits the strongest bond dissociation energy among these four Cr+⋅(N2)n (n = 1—4) complexes since it has the largest Cr+—N bond order. End-on structures and sequential bond dissociation energies of the Cr+·(N2)1-4 were studied using different DFT methods. The interaction in these complexes is of physical nature, where the di-ligated complex has the largest BDE. For tilted structure, [N·Cr·N]+, the interaction involves an electronic transfer from Cr+ to N (π-back donation).

Electron ionization of W(CO)6: Appearance energies

The electron ionization (EI) of W(CO)6 has been studied in detail using a high resolution crossed electron-molecular beams technique. We have detected singly (W+, CW+, (CO)xW+ (x=1–6), (CO)yCW+ (y=1–3), CO+) and doubly charge positive ions (W2+, CW2+, (CO)xW2+ (x=1–6) and (CO)yCW2+ (y=1–3)). The relative partial cross sections for formation of particular ions have been measured and the breakdown curves constructed. The ionization energies (IE) for single (8.47±0.06eV) and double ionization (22.90±0.08eV) of the molecule, as well as the appearance energies (AEs) for the dissociative ionization channels for singly and doubly charged ions have been estimated from experimental ion efficiency curves. On the basis of the IEs and AEs values we have calculated sequential bond dissociation energies (BDEs) of different bonds in the positive ions formed from W(CO)6.

Noncovalent Interactions of Zn+ with N-Donor Ligands (Pyridine, 4,4′-Dipyridyl, 2,2′-Dipyridyl, and 1,10-Phenanthroline): Collision-Induced Dissociation and Theoretical Studies

The binding interactions in complexes of Zn(+) with nitrogen donor ligands, (N-L) = pyridine (x = 1-4), 4,4'-dipyridyl (x = 1-3), 2,2'-dipyridyl (x = 1-2), and 1,10-phenanthroline (x = 1-2), are examined in detail. The bond dissociation energies (BDEs) for loss of an intact ligand from the Zn(+)(N-L)(x) complexes are reported. Experimental BDEs are obtained from thermochemical analyses of the threshold regions of the collision-induced dissociation cross sections of Zn(+)(N-L)(x) complexes. Density functional theory calculations at the B3LYP/6-31G* level of theory are performed to determine stable structures of these species and to provide molecular parameters needed for the thermochemical analysis of experimental data. Relative stabilities of the various conformations of these N-donor ligands and their complexes to Zn(+) as well as theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) and M06/6-311+G(2d,2p) levels of theory using the B3LYP/6-31G* optimized geometries. The experimental BDEs for the Zn(+)(N-L)(x) complexes are in reasonably good agreement with values derived from density functional theory calculations. BDEs derived from M06 calculations provide better agreement with the measured values than those based on B3LYP calculations. Trends in the sequential BDEs are explained in terms of sp polarization of Zn(+) and repulsive ligand-ligand interactions. Comparisons are made to the analogous Cu(+)(N-L)(x) and Ni(+)(N-L)(x) complexes previously studied.

Hydration Energies of Zinc(II): Threshold Collision-Induced Dissociation Experiments and Theoretical Studies

The first experimentally determined sequential bond dissociation energies of Zn(2+)(H(2)O)(n) complexes, where n = 6-10, are measured using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer coupled with an electrospray ionization source. Kinetic energy dependent cross sections are obtained and analyzed to yield 0 K threshold measurements for the loss of one and two water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. The threshold measurements are then converted from 0 to 298 K values to give the hydration energies for sequentially losing one water from each parent complex. Theoretical geometry optimizations and single-point energy calculations are performed using several levels of theory for comparison to experiment. Although different levels of theory disagree on the ground-state conformation of most complexes examined here leading to potential ambiguities in the final thermochemical values, calculations at the MP2(full) level provide the best agreement with experiment. On this basis, the present experiments are most consistent with the inner solvent shell of Zn(2+) being five waters, except for Zn(2+)(H(2)O)(6) where all waters bind directly to the metal ion. The charge separation process, Zn(2+)(H(2)O)(n) --> ZnOH(+)(H(2)O)(m) + H(+)(H(2)O)(n-m-1), which is in competition with the loss of water from the parent complex, is also observed for n = 6-8. These processes are analyzed in detail in the following paper.

Bond Dissociation Energies and Equilibrium Structures of Cu+(MeOH)x, x = 1−6, in the Gas Phase: Competition between Solvation of the Metal Ion and Hydrogen-Bonding Interactions

The solvation of Cu+ by methanol (MeOH) was studied via examination of the kinetic energy dependence of the collision-induced dissociation of Cu+(MeOH)x complexes, where x = 1-6, with Xe in a guided ion beam tandem mass spectrometer. In all cases, the primary and lowest-energy dissociation channel observed is the endothermic loss of a single MeOH molecule. The primary cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of multiple ion-neutral collisions, kinetic and internal energy distributions of the reactants, and lifetimes for dissociation. Density functional theory calculations at the B3LYP/6-31G* level are performed to obtain model structures, vibrational frequencies, and rotational constants for the Cu+(MeOH)x complexes and their dissociation products. The relative stabilities of various conformations and theoretical BDEs are determined from single-point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using B3LYP/6-31G*-optimized geometries. The relative stabilities of the various conformations of the Cu+(MeOH)x complexes and the trends in the sequential BDEs are explained in terms of stabilization gained from sd hybridization, hydrogen-bonding interactions, electron donor-acceptor natural bond orbital stabilizing interactions, and destabilization arising from ligand-ligand repulsion.

Density Functional and Ab Initio Study of Cr(CO)n (n = 1−6) Complexes

Cr(CO)n (n = 1-6) systems were studied for all possible spin states using density functional and high-level ab initio methods to provide a more complete theoretical understanding of the structure of species that may form during ligand dissociation of Cr(CO)6. We carried out geometry optimizations for each system and obtained vibrational frequencies, sequential bond dissociation energies (BDE), and total CO binding energies. We also compared the performance of various DFT functionals. Generally, the ground states of Cr(CO)6, Cr(CO)5, and Cr(CO)4, whose spin multiplicity is a singlet, are in good agreement with both previous theoretical results and currently available experimental data. Calculations on Cr(CO)3, Cr(CO)2, and CrCO provide new findings that the ground state of Cr(CO)3 might be a quintet with C2v symmetry instead of a singlet with C3v symmetry, and the ground state of Cr(CO)2 is not a linear quintet, as suggested by previous DFT calculations, but rather a linear septet. We also found that nonet states of Cr(CO)2 and CrCO display partial C-O bond breakage.

Noncovalent Interactions of Cu+ with N-Donor Ligands (Pyridine, 4,4-Dipyridyl, 2,2-Dipyridyl, and 1,10-Phenanthroline): Collision-Induced Dissociation and Theoretical Studies

Collision-induced dissociation of complexes of Cu+ bound to a variety of N-donor ligands (N-L) with Xe is studied using guided ion beam tandem mass spectrometry. The N-L ligands examined include pyridine, 4,4-dipyridyl, 2,2-dipyridyl, and 1,10-phenanthroline. In all cases, the primary and lowest-energy dissociation channel observed corresponds to the endothermic loss of a single intact N-L ligand. Sequential dissociation of additional N-L ligands is observed at elevated energies for the pyridine and 4,4-dipyridyl complexes containing more than one ligand. Ligand exchange processes to produce Cu+Xe are also observed as minor reaction pathways in several systems. The primary cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level are performed to obtain model structures, vibrational frequencies, and rotational constants for the neutral N-L ligands and the Cu+(N-L)x complexes. The relative stabilities of the various conformations of these N-L ligands and Cu+(N-L)x complexes as well as theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using B3LYP/6-31G* optimized geometries. Excellent agreement between theory and experiment is observed for all complexes containing one or two N-L ligands, while theory systematically underestimates the strength of binding for complexes containing more than two N-L ligands. The ground-state structures of these complexes and the trends in the sequential BDEs are explained in terms of stabilization gained from sd-hybridization and repulsive ligand-ligand interactions. The nature of the binding interactions in the Cu+(N-L)x complexes are examined via natural bond orbital analyses.

An experimental and theoretical investigation into the binding interactions of silver cluster cations with ethene and propene

Sequential bond dissociation energies (BDEs) and association entropies for the attachment of C 2H 4 ligands to ground-state Ag m + ( m = 3–13) clusters and for the attachment of C 3H 6 ligands to ground-state Ag m + ( m = 3–9) clusters have been measured using temperature-dependent equilibrium methods. Variations in metal–ligand BDEs are examined in detail both as a function of sequential ligand addition to a given Ag m + cluster and as a function Ag m + cluster size for the first ligand additions. With the exception of the Ag 6 + and Ag 7 + clusters, BDEs for the loss of a ligand from the Ag m +(L) ( m = 3–13, L = C 2H 4; m = 3–9, L = C 3H 6) clusters decrease as the size of the silver clusters increase. Electronic structure calculations at the DFT-B3LYP level were performed in order to determine the vibrational frequencies, rotational constants and geometries of the silver–alkene clusters of interest as well as the nature of the bonding of these clusters and its variation with core ion coordination.

Solvation of copper ions by imidazole: Structures and sequential binding energies of Cu+(imidazole)x, x = 1–4. Competition between ion solvation and hydrogen bonding

The sequential bond dissociation energies of Cu+(imidazole)x, where x = 1-4 are determined by analysis of the kinetic energy dependence of the collision-induced dissociation with Xe in a guided ion beam tandem mass spectrometer. In all cases, the primary and lowest energy dissociation channel observed is the endothermic loss of an intact imidazole molecule. The primary cross section thresholds are interpreted to yield 0 K and 298 K bond dissociation energies after accounting for the effects of multiple ion-neutral collisions, kinetic and internal energy distributions of the reactants, and dissociation lifetimes. To obtain model structures, vibrational frequencies, rotational constants and energetics for the Cu+(imidazole)x complexes and their dissociation products, density functional theory calculations at the B3LYP/6-31G* level are performed. Theoretical bond dissociation energies are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using the B3LYP/6-31G* optimized geometries. Excellent agreement between theory and experiment is observed for the Cu+(imidazole)x complexes, where x = 1, 2 and 4. In contrast, theory systematically underestimates the strength of the binding in the Cu+(imidazole)3 complex. The ground state structures of the Cu+(imidazole), complexes and the trends in the sequential bond dissociation energies are explained in terms of stabilization gained from sd hybridization and hydrogen bonding interactions and destabilization arising from ligand-ligand repulsion. The trends in the binding of these complexes are also examined to provide insight into the structural and functional roles that histidine and other ligands play in the behavior of metalloproteins and metalloenzymes.

Bond dissociation energies and structures of CuNO(+) and Cu(NO)(2)(+).

The bond dissociation energies of CuNO(+), Cu(NO)(2)(+), and CuAr(+) are determined by means of guided ion beam mass spectrometry and quantum chemical calculations. From the experiment, the values D(0)(Cu(+)-NO) = 1.13 +/- 0.05, D(0)(ONCu(+)-NO) = 1.12 +/- 0.06, D(0)(Cu(+)-Ar) = 0.50 +/- 0.07, and D(0)(Cu(+)-Xe) = 1.02 +/- 0.06 eV are obtained. The computational approaches corroborate these results and provide additional structural data. The relative values of D(0)(Cu(+)-NO) and D(0)(Cu(+)-Xe) are consistent with the approximately thermoneutral formation of CuXe(+) upon interacting CuNO(+) with xenon. The sequential bond dissociation energies of Cu(NO)(2)(+) exhibit a trend similar to those of other Cu(I) complexes described in the literature. Although metathesis of nitric oxide to N(2) and O(2) is of considerable interest, no evidence for N-N- or O-O-bond formations in Cu(NO)(n)(+) ions (with n up to 3) is obtained within the energy range studied experimentally.

Absolute Binding Energies of Alkali-Metal Cation Complexes with Benzene Determined by Threshold Collision-Induced Dissociation Experiments and ab Initio Theory

The sequential bond dissociation energies (BDEs) of the mono- and bis-benzene complexes with alkali metal cations (Li+, Na+, K+, Rb+, and Cs+) are determined experimentally by collision-induced dissociation (CID) with Xe in a guided ion beam mass spectrometer and theoretically by ab initio calculations. The kinetic energy dependence of the CID cross sections are analyzed to yield 0 and 298 K bond energies for (C6H6)x-1M+−C6H6 (x = 1−2) after accounting for the effects of the internal energies of the reactant ions, the multiple collisions of the ions with xenon, and the dissociation lifetimes of the ionic complexes. Ab initio binding energies are calculated at the MP2(full)/6-311+G(2d,2p)//MP2(full)/6-31G* level and corrected for zero-point energies (ZPE) and basis set superposition errors (BSSE). The theoretical BDEs are in reasonably good agreement with the experimentally determined 0 K bond energies when full electron correlation is included (for Li+, Na+, and K+) but differ appreciably when effective c...

Alkali ion carbonyls: sequential bond energies of Li +(CO) x ( x = 1−3), Na +(CO) x ( x = 1, 2) and K +(CO)

The sequential bond dissociation energies for Li +(CO) x ( x = 1−3), Na +(CO) x ( x = 1,2), and K +(CO) are determined by examining the collision-induced dissociation reactions with argon in a guided ion beam mass spectrometer. Analysis of the kinetic energy dependent cross sections yield values for the (CO) x−1 M +CO bond dissociation energies (BDEs) of 0.57 ± 0.13, 0.37 ± 0.04 and 0.36 ± 0.04 eV for M  Li ( x = 1–3, respectively), 0.33 ± 0.08 and 0.25 ± 0.03 eV for M  Na ( x = 1 and 2, respectively), and 0.19 ± 0.05 eV for K +CO. In addition, the M +Ar BDEs are determined by examining the ligand exchange reaction of M +(CO) with Ar and are found to be 0.34 ± 0.14, 0.16 ± 0.09 and 0.14 ± 0.07 eV for M  Li, Na and K, respectively. The trends in BDEs can be explained readily in terms of electrostatic bonding interactions. A comparison of the alkali metal ion—CO BDEs with those of transition metal ion carbonyls reveals the contributions of s-dσ hybridization and d-π ∗ back-donation in the chemical bonding of the latter systems.

Sequential Bond Dissociation Energies of M+(NH3)x (x = 1−4) for M = Ti−Cu

The sequential bond dissociation energies (BDEs) for M+(NH3)x (x = 1−4) for M = Ti−Cu are determined by examining the collision-induced dissociation reactions with xenon in a guided ion beam mass spectrometer. In the cases of Fe, Co, Ni, and Cu, the BDE for the second ammonia molecule is determined to be greater than the BDE for the first ammonia molecule. For all metal ions but Ti+, the BDEs for the first two ammonia molecules are large in comparison to the BDEs for the third and fourth ammonia molecules. In general, the results of this study for the BDEs of the first and second ammonia molecules agree well with the results of previous experimental and theoretical studies. Previous studies are available only for M+(NH3)3 (M = V, Mn, Ni, and Cu) and M+(NH3)4 (M = V and Cu) complexes, such that this study provides the first determination of all other (NH3)2M+−NH3 and (NH3)3M+−NH3 BDEs. The trends in BDEs are discussed in terms of hybridization, dative interactions, and spin changes and compared to trends for other comprehensively studied ligands, H2O and CO.

A molecular beam photoionization mass spectrometric study of Cr(CO)6, Mo(CO)6, and W(CO)6

The photoionization efficiency (PIE) spectra for M(CO)n+ (n=0–6) from M(CO)6, M=Cr, Mo, and W, have been measured in the photon energy range of 650–1600 Å. Based on the ionization energies for M(CO)6 and appearance energies (AEs) for M(CO)n+ (n=0–5) determined here, we have obtained estimates for the sequential bond dissociation energies (D0) for CO–M(CO)n−1+ (n=1–6). The comparison between the D0 values for the Cr(CO)6+ system obtained here and in the recent collisional induced dissociation and theoretical studies suggests that D0 values for CO–M(CO)n−1+ (n=3–6) based on this PIE experiment are reliable. The PIE results reveal the general trend for individual D0 values that D0[CO–Cr(CO)n−1+]<D0[CO–Mo(CO)n−1+]<D0[CO–W(CO)n−1+] (n=3–6). The comparison of the first D0 values for M(CO)6+ obtained here and those for M(CO)6 reported previously provides strong support for the theoretical analysis that the importance of relativistic effects, which give rise to more efficient M to CO π-back-donation in M(CO)6, is in the order W(CO)6>Mo(CO)6>Cr(CO)6.

Accurate Borane Sequential Bond Dissociation Energies by High-Level ab Initio Computational Methods

Ab initio molecular orbital calculations at the G-2 and CBS-4 compound levels of theory were used to determine the sequential homolytic bond dissociation energies (BDE's) for a series of B−H, B−C, and B−F bonds in a variety of cyclic and acyclic boranes. The calculated average BDE's agreed very well with the limited experimental data available. However, the first sequential BDE's, which are the most relevant for understanding borane reactivity, were substantially higher than the average BDE's. In general, first BDE's were found to be larger for B−C and B−H bonds in organoboranes than for C−C and C−H bonds in hydrocarbons, even though average B−H and B−C BDE's are lower than average C−H and C−C BDE's. In all the boron substitution patterns examined, B−H and B−C bonds were found to be of almost identical strength, while B−F bonds were found to be much stronger. Moreover, the strengths of B−H and B−C bonds were found to be essentially independent of the electronegativity, π-donating ability, and conjugative ...

First Transition Metal-Boryl Bond Energy and Quantitation of Large Differences in Sequential Bond Dissociation Energies of Boranes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFirst Transition Metal-Boryl Bond Energy and Quantitation of Large Differences in Sequential Bond Dissociation Energies of BoranesPaul R. Rablen, John F. Hartwig, and Steven P. NolanCite this: J. Am. Chem. Soc. 1994, 116, 9, 4121–4122Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 May 1994https://doi.org/10.1021/ja00088a075RIGHTS & PERMISSIONSArticle Views854Altmetric-Citations58LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (318 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts