Theoretical Study of SalicylaldehydeConformal Isomers and TheirIntramolecular Oxygen and HydrogenRelations

CHENG CHEN, SHUANG-FUH SHYU, FU-SHENG HSUDepartment of Applied Chemistry, Chung-Cheng Institute of Technology, Ta-hsi, Taoyuan 33509,Taiwan Republic of China

Received 2 November 1998; revised 18 March 1999; accepted 7 April 1999

ABSTRACT: To verify the semiempirical-type localized hydrogen bonding analysismethods introduced by us several years ago, the intramolecular oxygen and hydrogenrelations within salicylaldehyde are selected as the major topic in this theoretical study.The B3LYPr6-31G** density functional method is chosen for both the full-optimizationand frequency-type calculations. Four ortho-type planar conformal isomers are proven tobe local minima, and four internal rotation transition states are found by QST3-typecalculation. The special interpretations of —CHO and —OH characteristic frequencies,energy barriers, and thermal chemical results are discussed. In the semiempirical scheme,both local hydrogen bonding population analysis and localized hydrogen bond energybreaking procedures are applied to five pairs of related oxygen and hydrogen atoms ineach isomer. The explanations for the strong or weak hydrogen bonds and intra-CHOrepulsion relationships are discussed. Q 1999 John Wiley & Sons, Inc. Int J Quant Chem 74:395]404, 1999

Key words: intramolecular oxygen and hydrogen relations; B3LYPr6-31G**; localizedhydrogen bonding analysis; salicylaldehyde

Correspondence to: C. Chen.Contract grant sponsor: National Science Council, Republic

of China.Contract grant number: NSC-87-2113-M-014-001.

( )International Journal of Quantum Chemistry, Vol. 74, 395]404 1999Q 1999 John Wiley & Sons, Inc. CCC 0020-7608 / 99 / 040395-10

CHEN, SHYU, AND HSU

Introduction

ince Chen et al. originally introduced theS semiempirical localized analysis method of hy-w xdrogen bonding in 1994 1 , this method has been

successfully applied to intramolecular hydrogen-bonding problems of various molecular systemsw x2]11 . These localized calculations of bond orderŽ . Ž .P and bond energy BE to determineO ??? H O ??? Hhydrogen bonding are quite different from theconventional treatments of intramolecular hydro-

w xgen-bonding problems in recent works 12]19 .The localized analysis method is not only a directand intuitive method for identification of both

intermolecular or intramolecular hydrogen bonds,but it is also a fast and generalized method toidentify all the inter oxygen hydrogen relation-ships within any kind of molecular system. InTable I we show several of our former calculations

Ž . Ž .for bond order P and bond energy BEO ??? H O ??? Hof various molecular systems for comparisonw x1]10 . It is found that some intramolecular hydro-gen bonds such as salicylic acid, cis-hydrogen

w Ž . Ž .xacrylic acid CH OH 5CH COOH , and b-hy-Ž Ž . .droxyacrolein CH OH 5CHCHO are much

stronger than the intermolecular hydrogen bonds,such as H O ??? HF. All forms of carboxylic acid,2RCOOH, have the intra-COOH weak hydrogenbond, where localized energies and bond ordersrange between 10 and 14 kJrmol and 0.06 and

TABLE I( )Comparison of bond order P and bond energy BE kJ ///// mol .O ??? H O ??? H

Type of H Bond Molecules H Bond P BE ReferenceO ??? H O ??? H

Intermolecular H O, HF H O ??? HF 0.221 47.79 12 2H bond between H O, NH H O ??? HNH 0.111 16.59 12 3 2 2molecules

Interfunctional o-Nitrophenol }NO ??? HO } 0.147 44.62 1, 220.091 19.52 1, 2group H bond o-Nitroaniline }NO ??? HN }2 2

in a molecule HOxalic acid 0.153 30.80 5O O

C CO O

H( ) 0.238 70.69 8Salicylic acid R OH

0.236 68.07 7( ) ( )cis-CH OH CH COOH H O RO C 0.294 85.15 9( ) ( )CH OH CHCHO R H

O H OCHO } COOH 0.116 19.72 10OPyruric acid 0.145 28.31 10C CH

O(Intra-CO H RCOOH R H, CH , C H , 0.063; 10.15; 6C H2 3 2 5

O)H bond in a and C H 0.071 12.256 5molecule Oxalic acid 0.068 11.76 5

Salicylic acid 0.076 14.06 8( ) ( )cis-CH OH CH COOH 0.077 14.14 7

CHO } COOH 0.068 11.08 10Pyruric acid 0.068 11.09 10

OIntra-CHO o-Nitrobenzoaldehyde y0.200 y63.50 2, 3C

repulsion in a o-Aminobenzoaldehyde y0.225 y76.29 2, 3H( )molecule o-C H CHO y0.223 y74.25 2, 36 4 2

CHO } COOH y0.213 y61.35 10( )CH OH CHCHO y0.207 y70.87 10

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SALICYLALDEHYDE CONFORMAL ISOMERS

0.08, respectively. Both are less than the lowestlimits of intermolecular hydrogen bonding, as

w xshown in Ref. 1 . The most interesting inter-oxygenhydrogen atom relationship in Table I is the intra-CHO repulsion relationship in the various alde-hyde molecules. Although the interatomic distancebetween O and H in a —CHO group is around 2.0A, which is very close to the hydrogen-bonding distance, there is no bonding between Oand H. On the other hand, the significant negativevalues of P and BE indicate that intra-O ??? H O ??? HCHO groups O and H have strong repulsive forces.To verify both the strong intramolecular hydrogenbonding and the CHO-type strong repulsive effectin the same molecular system, we selected thesalicylaldehyde molecule for our theoretical studyin this work. In addition, due to the delocalizationeffect, all the conformal isomers of this ortho-typemolecule have planar structures and only four of

w xthem could be found 12]19 . Consequently, thistheoretical study is easy to handle with very littlecomplexity. Because no experimentally observedgeometrical data can be found for all the isomersand we want to start our work with the samestandard geometrical data, we chose one of themost reliable ab initio or density functional theoryŽ . Ž .DFT molecular orbital MO methods to findmolecular geometries, relative energies, and theirinternal rotational transition states for these fourconformal isomers. Afterward, with this relativelyreliable molecular geometry, we proceeded with

w xour semiempirical MO calculation 1 and appliedlocalized analysis between oxygen and hydrogenatoms for various isomers of salicylaldehyde.

Calculation Methods

B3LYP / 6-31G** MO CALCULATION

w xAs shown in most recent reports 20]24 DFThas been successful in predicting various molecu-lar properties better than or comparable to thesecond-order Moller]Plesset perturbation methodŽ .MP2 , for a cost that is substantially less than thatof traditional correlation techniques. In addition toour former MP2r6-31G**-type study of salicyl-

w xaldehyde 11 , we selected the DFT-type B3LYPr6-31G** calculation method from the Gaussian 94

w xpackage 25 for optimization and vibrational fre-quency calculations to establish reliable structuresin this work. Four planar-type conformal isomer

structures are proved by the full-optimization andvibration frequency procedures. These isomerswere defined to be L , L , L , and L according to1 2 3 4the order of molecular energies L < L - L -1 2 3L . These structures, their five pairs of important4long-range interatomic distances between O andH, and their related charge densities are given inFigure 1. To determine the relative stability ofrigidity of these isomers, we applied the option of

w xQST3 26]28 by variation of the dihedral anglesD for the internal rotation of the CHOŽO5 C —C 5 C.functional group and by variation of the dihedralangle D for the internal rotation of theŽHO—C 5 C.—OH group. Four saddle point internal rotationaltransition states were found by this procedure. Inthese transition states, T is the saddle point be-13tween L and L via internal rotation of the —CHO1 3group, T is the saddle point between L and L14 1 4via internal rotation of the —OH group, T is the42saddle point between L and L via internal rota-4 2tion of the —CHO group, and T is the saddle32point between L and L via internal rotation of3 2the —OH group. The calculation D H and DG allrefer to L at 298.15 K and all are in Table II for1comparison.

LOCALIZED-TYPE ANALYSIS BETWEENO AND H

The most important subject in this work is tofind the direct interatomic relations between vari-ous O and H atoms in the salicylaldehydemolecule. There are two parameters between fivesets of O ??? H relations, which should be able to bedetermined out directly from B3LYPr6-31G** cal-culation. The first parameter, the interatomic dis-

Ž .tance d was directly selected from the fullO ??? Hoptimized geometry of B3LYPr6-31G** calcula-tions, as shown in Figure 1. The second parameter,

Ž .the coulombic attraction energy yE , is di-O ??? Hrectly calculated with d and charge densitiesO ??? H

Ž . Ž .of O Q and H Q of the B3LYP results:O H

Q QO HE s .O ??? H dO ??? H

However, with the above-mentioned two B3LYPparameters, we cannot get any additional informa-

˚tion, except d s 1.7300 A and yE sO ??? H O ??? H9 10 9 10

134.62 kJrmol for the strongest intramolecular hy-drogen bonding of the L isomer.1

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CHEN, SHYU, AND HSU

FIGURE 1. Stable structures, inter O ??? H distances, and their electron densities of salicylaldehyde.

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TABLE II( )Relative thermal energies kJ ///// mol of

salicylaldehyde conformal isomers and theira( )transition states at 298.15 K .

Dihedralb bType Form DH DG angle

Local minima L 00.00 00.001L 38.38 35.082L 43.27 39.573L 49.65 46.504

Transition state T 77.69 76.48 96.59813T 63.22 60.91 109.45814T 52.93 51.12 88.33832T 75.93 74.77 80.59842

aThe optimized energies of L are DH = y420.694169 a.u.,1DG = y420.733244 a.u.b1 a.u.= 2625.5 kJ / mol; all refer to energies of related L1( )in kJ / mol .

To distinguish various kinds of inter —O ??? Hrelationships, we have to apply the semiempirical-type localized analysis method for bond energyŽ . Ž .BE and bond order P :O ??? H O ??? H

Ž . Ž .BE s f D E q f D E y E .O ??? H O O H H O ??? H

In the above equation, D E and D E are theO Hdifferent atomic energies before and after the MOcalculation; E is the sum of energies betweenO ??? Hall of the diagonal energy matrix elements:

E EO ??? H O ??? Hf s and f s ,O HBonds BondsÝ E Ý EX O ??? H X X ??? H

w xas shown in our former work 1]10 .

P s " P 2 q P 2žO ??? H 2 s , 1 s 2 p , 1 sO H x HO

1r22 2qP q P ./2 p , 1 s 2 p , 1 sy H z HO O

TABLE IIILocalized analysis between oxygen and hydrogen relationship of salicylaldehyde.a

O ??? H d yE BEO ??? H O ??? H O ??? H

˚( ) ( ) ( )relation Isomer A kJ / mol P kJ / molO ??? H

bO ??? H L 1.7300 134.62 0.231 57.139 10 1 (1) (1) (1) (1)inter L 5.0042 38.28 0.012 6.072 (4) (4) (3) (4)OH ??? O5C L 3.6943 51.08 0.005 7.853 (2) (2) (4) (2)

L 3.7148 48.54 0.016 7.034 (3) (3) (2) (3)

O ??? H L 3.9546 16.96 0.031 0.378 11 1 (3) (2) (2) (4)inter L 2.4340 27.79 0.033 0.892 (1) (1) (1) (1)HO ??? H—CO L 2.6281 8.34 0.020 0.893 (2) (4) (3) (1)

L 3.9935 9.61 0.012 0.894 (4) (3) (4) (1)

O ??? H L 3.9173 16.47 0.018 1.269 12 1 (4) (3) (4) (3)inter L 2.5072 28.65 0.035 2.752 (2) (1) (1) (1)—C5O ??? H—C L 2.5025 28.46 0.034 2.613 (1) (2) (2) (2)

L 3.8332 14.47 0.021 1.154 (3) (4) (3) (4)

O ??? H L 2.5809 31.71 y0.059 y3.098 15 1 (2) (2) (3) (1)inter L 2.6686 23.48 y0.056 y6.442 (4) (3) (1) (3)

HO ??? H—C L 2.5235 31.98 y0.060 y4.623 (1) (1) (4) (2)L 2.6512 22.24 y0.056 y7.174 (3) (4) (1) (4)

O ??? H L 2.0248 28.50 y0.218 y72.819 11 1 (4) (1) (1) (2)intra L 2.0240 25.69 y0.225 y72.672 (3) (2) (2) (1)—CHO L 2.0088 8.30 y0.231 y80.403 (1) (4) (3) (4)

L 2.0229 14.93 y0.239 y76.954 (2) (3) (4) (3)

aSubscript numbers in parentheses indicate hydrogen bond strength.b ˚ [ ]Experimental value is 1.7400 A; Ref. 13 .

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CHEN, SHYU, AND HSU

The P matrix elements of mth and n th AO’s inmn

the preceding equation can be calculated directlyby semiempirical MO method, where the plus orminus sign selection of P is dependent on theO ??? Hsign of BE , as calculated. The atomic distanceO ??? HŽ . Ž .d , coulombic attraction energy yE ,O ??? H O ??? H

Ž . Ž .bond energy BE , and bond order P ofO ??? H O ??? Hthe five O ??? H sets are calculated and listed inTable III and discussed in the following.

Results and Discussion

ENERGIES AND POTENTIAL BARRIERS OFB3LYP / 6-31G**

From the molecular energy and energy barriercalculations of Table II, the orders of stability areshown to be L 4 L ) L ) L . The strongest1 2 3 4hydrogen bond inside L causes its molecular en-1ergy to be significantly lower than all the otherisomers and transition states. The internal rotationbarriers of the —CHO group for the four isomersare 77.69 kJrmol for L , 37.55 kJrmol for L , 34.421 2kJrmol for L , and 26.28 kJrmol for L . The inter-3 4nal rotation barriers of —OH are 63.22 kJrmol forL , 14.55 kJrmol for L , 9.66 kJrmol for L , and1 2 313.57 kJrmol for L . The optimized dihedral angle4of the transition states is usually a little close to the

dihedral angle of the high-energy isomer. The cal-culated barrier peaks of L are significantly larger1than the related internal rotation barriers of theother three isomers. These calculated barrierheights of L are also greater than the lower limit1value of 30 kJrmol, which was reported from theelectron diffraction experiments of Borisenko et al.w x14 . All the results of the molecular energy andenergy barrier calculations show that L , with its1strong hydrogen bond, is the most stable isomer.The L isomer, with weak hydrogen bonds, is the2second most stable molecule within the isomers.

CHARACTERISTIC FREQUENCIES AND BONDDISTANCES OF —CHO AND —OH

Within the 39 vibrational modes, the twostretching-type characteristic frequencies of—CHO and —OH are most important for theexplanation of the strong intramolecular hydro-gen-bonding problem. These two vibrational fre-quencies and the related observed and calculated

w xreference values 13]16 are listed in Table IV. Bymaking a close comparison between vibration andmolecular geometry, we also determine the calcu-lated bond distances d and d , as well asC 5 O O — Htheir related observed and theoretical referencevalues from this table. In addition to these results

TABLE IV˚ y1( ) ( )Bond distances A and characteristic frequencies cm related to hydrogen bonds.

B3LYP MP2

CHO group OH group CHO group OH group

Form d n d n d n d nC5 O CHO OH OH C5 O CHO OH OH

L1Calculated 1.235 1733 0.990 3360 1.240 1744 0.981 3561Observed 1.225 " 0.004 1682 0.985 " 0.014 3190 1.225 " 0.004 1682 0.985 " 0.014 3190

Scale factor 0.97 0.95 0.96 0.90L 1.220 1783 0.966 3822 1.229 1758 0.966 38782L 1.217 1787 0.966 3820 1.228 1760 0.964 39013L 1.214 1806 0.967 3802 1.224 1772 0.967 38564

PhenolCalculated 0.966 3824 0.965 3881

aObserved 0.958 " 0.003 3655 0.958 " 0.003 3655Scale factor 0.96 0.94

BenzaldehydeCalculated 1.216 1799 1.2267 1768

aObserved 1.212 " 0.003 1730 1.212 " 0.003 1730Scale factor 0.96 0.98

a [ ]Refs. 14]17 .

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SALICYLALDEHYDE CONFORMAL ISOMERS

of salicylaldehyde, the calculated and observedvalues of phenol and benzaldehyde are also listedin the same table to show the influence of theintramolecular hydrogen-bonding effect in salicyl-aldehyde. Comparison of the calculated bond dis-tances and vibrational frequencies with the related

w xexperimental observed values of Refs. 14]17shows that most of the B3LYPr6-31G** results are

w xbetter than the MP2r6-31G** results of Ref. 11 .The scale factor f of vibrational frequencies iscalculated by

observed frequencyf s .

calculated frequency

Both the B3LYPr6-31G** of this work, 0.95 F fF 0.97, and the MP2r6-31G** of our former work,0.90 F f F 0.98, match reasonably well with the f

w xvalues reported by Foresman et al. 17 . With thesecalculated reliable frequencies and bond distances,one may easily determine that the non-hydrogen-bonded or weak hydrogen-bonded isomers L , L ,2 3and L are very close to the related results of4phenol or benzaldehyde. However, the results ofisomer L within the strong hydrogen-bonded sys-1tem are quite peculiar, as shown in Table IV. Bothd and d distances are significantly largerC 5 O O—Hthan the results of the phenol, benzaldehyde, orother isomers. On the other hand, the two charac-teristic vibrational frequencies of isomer L are1significantly smaller than the related frequenciesof phenol, benzaldehyde, or the other isomers. Thedecreasing frequencies and the lengthening bonddistances of —CHO and —OH are both createddue the intramolecular hydrogen bond formationbetween these two function groups.

One of the interesting additional problems inthe above-mentioned characteristic vibrationalmodes is determining which atoms are involved inthis vibration. We collected the vibrational Carte-sian coordinates from B3LYPr6-31G** output and

2 2Ž'calculated the absolute coordinates x q y for.planar molecules of each atom for various vibra-

tional modes. The absolute values of atoms are ofinvariant quantity, which is independent of coordi-nate selection of an atom in a molecule if thefull-optimized geometry is fixed. The absolute co-ordinates for —CHO characteristic vibration and—OH characteristic vibration are listed in Table V.The reason we define the characteristic frequencyof the —CHO group as n instead of n is— CHO C 5 Obecause the relative ratio of the absolute coordi-

nates of C, H, and O is approximately 0.7 : 0.5 : 0.5for both benzaldehyde and the isomers L , L , and2 3L . In addition, the participation of the atomic4absolute coordinate of the H atom in —CHO isvery significant in this vibrational mode. The mostinteresting problem is finding the absolute coordi-nates of the atoms C, H, O, and H of the OH groupshown in the —CHO vibrational motion of L ,1where the relative ratios for these four atoms inthe table are 0.55 : 0.54 : 0.33: 0.43. If we comparethe contribution of H in OH of all the isomers ofthe molecule from L to L , the absolute coordi-1 4nates are 0.43 : 0.02 : 0.05 : 0.06. These results indi-cate not only that the strong hydrogen bond leadsto bond distance elongation and frequency de-crease but also that the motion of H in OH issignificantly involved in the —CHO characteristicvibrational mode of the isomer L .1

LOCALIZATION ANALYSIS BETWEENVARIOUS O AND H

The objective of location analysis is both topredict the location of hydrogen bonds by indirectinformation of molecular energies or characteristicfrequencies and to determine the direct inter-atomic relationships between oxygen and hydro-gen atoms by localization-type analysis. With thiskind of analysis, one may determine locationswithin various isomers of strong hydrogen bonds,weak O ??? H bonding, or repelling-type O ??? H re-lations. As shown in Figure 1 and Table III, thereare five pairs of long-range adjacent-type O ??? Hinteratomic relations selected for localization anal-ysis in this work. The first pair is formed by theO of —CHO and the H of —OH, which is definedas O ??? H . The second pair is formed by the O9 10of —OH and the H of —CHO, which is definedas O ??? H . The third pair is formed by the O8 11of —CHO and the adjacent H on the aromaticring, which is defined as O ??? H . The fourth9 12pair is formed by the O of —OH and the adja-cent H on the aromatic ring, which is defined asO ??? H . The fifth pair contains the O and H of8 15the —CHO group, and this intra-CHO group rela-tion is defined as O ??? H .9 11

We applied the method shown in the calcula-tion section to calculate d , yE , BE ,O ??? H O ??? H O ??? Hand P for these five sets of O ??? H isomers,O ??? Hand all of them are listed in Table III for compari-son. Due to the strong electron-donating effect ofO in —CHO and electron-accepting effect of H in

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 401

CHEN, SHYU, AND HSU

TABLE VThe most important Cartesian coordinates and their absolute values of n and n .CHO OH

n nCHO OH

2 2 2 2' 'Form Atom X Y X q Y X Y X q Y

L C 0.55 0.00 0.551H y0.40 0.36 0.54 y0.55 0.83 1.00O y0.33 y0.03 0.33 0.03 y0.05 0.06

( )H of OH y0.41 y0.14 0.43

L C y0.37 0.56 0.672H y0.21 y0.52 0.56 y0.52 0.85 1.00O 0.26 y0.35 0.44 0.03 y0.05 0.06

( )H of OH y0.02 0.00 0.02

L C y0.40 0.59 0.713H y0.12 y0.46 0.48 0.28 0.96 1.00O 0.28 y0.37 0.46 y0.02 y0.06 0.06

( )H of OH 0.05 y0.01 0.05

L C 0.70 y0.08 0.704H y0.23 0.43 0.49 0.23 0.97 1.00O y0.47 0.03 0.47 y0.02 y0.06 0.06

( )H of OH y0.06 0.00 0.06

Benzaldehyde C 0.63 y0.31 0.70H y0.07 0.50 0.50O y0.43 0.18 0.47

Phenol H 0.92 y0.38 1.00O y0.06 0.02 0.06

—OH, the most important bonding effect is cre-ated by the O ??? H relation. Even in the long9 10d and the small bond order P cases for L ,O??? H O ??? H 2L , and L , the coulombic attraction energy3 4yE and the localized bond energy BE areO ??? H O ??? Hnot negligibly small. The only strong hydrogenbond in the isomers is O ??? H of L . Comparing9 10 1the P s 0.231 and E s 57.13 kJrmol ofO ??? H O ??? Hthis hydrogen bond with the former calculated

w xvalues of Refs. 1]10 in Table I, it is easily seenthat this hydrogen bond is stronger than the otherintermolecular hydrogen bonds, as well as theintramolecular hydrogen bonds of o-nitrophenol,and oxalic acid. However, this hydrogen bond isweaker than the strong hydrogen bonds of malon-

Ž . Ž .aldehyde, cis-CH OH 5CH COOH , and salicylicacid, in comparison to both P and BE ofO ??? H O ??? HTable I.

In our former salicylic acid calculation, theO ??? H formed with the O of OH and the H ofCOOH is the second important hydrogen bond.On the other hand, the O ??? H of the L or L8 11 2 3

isomers in this molecule of salicylaldehyde in thiswork are very weak, even weaker than the O9??? H formed by the O of —CHO and the H12aromatic ring in the cases of isomers L and L .2 3Both the P and BE of O ??? H and OO ??? H O ??? H 9 12 8??? H for L and L are very small, with P F11 2 3 O ??? H0.035 and E F 2.75 kJrmol. All these are lessO ??? Hthan the intra-COOH type O ??? H relation, asshown in Table I. However, comparing the PO ??? Hor BE of O ??? H or O ??? H , their rankingO ??? H 9 12 8 11order follows L ) L ) L , which matches very2 3 4well with the numerical order of energy barriers ormolecular energy. This trace amount of weakO ??? H interatomic relation is positively correlatedwith the relative stability among L , L , and L .2 3 4According to the P and BE calculation,O ??? H O ??? Hboth O ??? H and intra-CHO type O ??? H are8 15 9 11repulsive-type neglect values. Especially, the intra-CHO type O ??? H is strongly repelling, which is9 11very characteristic, with a d of O ??? H ofO ??? H 9 11

˚about 2.0 A, y0.24 F P F y0.20 and y80.0O ??? HkJrmol F BE F y60.0 kJrmol for the isomersO ??? H

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SALICYLALDEHYDE CONFORMAL ISOMERS

of salicylaldehyde and the other aldehyde com-pounds shown in Table I. These repelling relations

Ž .cannot be determined by bond distance d orO ??? HŽ .coulombic attraction energy yE . In intra-O ??? H

CHO type O ??? H , where O and H are usually9 11Ž . Ž .formed with short d with small yE ,O ??? H O ??? H

this inter O ??? H relationship is quite different fromŽ .the short d with large yE of the strongO ??? H O ??? H

hydrogen-bonding cases.

Summary and Conclusions

Similar to our former MP2r6-31G**-type calcu-w xlation 11 , four planar conformal isomers L , L ,1 2

L , and L forming four transition states T , T ,3 4 13 14T , and T are found by B3LYPr6-31G** full32 42optimization and QST3 optional optimization.Comparing molecular energies and energy barri-ers, the structure L with strong bonding effect is1seen to be more stable and rigid than any of theother three isomers.

The strong bonding effect may be indirectlyexplained by the decreasing characteristic frequen-cies n and n or explained by the elongationCHO OHof d and d , as shown in Table IV. TheC 5 O OH

2 2Ž .'absolute coordinates x q y of n and nCHO OHare studied for various isomers, which are re-ported in Table V. A most interesting result is that

2 2'the x q y values of H of OH in the n -typeCHOmotion are very large and significant in the stronghydrogen-bonded L case. This is another piece of1evidence to indicate that the hydrogen-bondingeffect is involved in the molecular vibrational modeof n .CHO

Having determined the reliable optimized ge-ometry of B3LYPr6-31G** and substituting thatinto semiempirical MO and localized bond orderŽ . Ž .P and bond energy BE , we proceedO ??? H O ??? Hwith the analysis of five pairs of O and H invarious isomers. There are three important resultswhich may be concluded from this analysis:

1. With shortest d and largest yE ,O ??? H O ??? HBE , and P , the O ??? H of L is theO ??? H O ??? H 9 10 1only strong hydrogen bond in this molecularsystem, even stronger than the ordinary in-termolecular hydrogen bond, as can be seenby comparing these results with the BEO ??? Hand P of Table I.O ??? H

2. The trace of weak O ??? H bonding relationsin the high-energy isomers L , L , and L2 3 4

predicted the order of stability L ) L ) L ,2 3 4which matches well with the order of ener-gies and potential barriers.

3. The O ??? H and O ??? H are repelling8 15 9 11relations between O and H. Particularly, theintra-CHO-type O ??? H with short d ,9 11 O ??? Hsmall yE , negative P , and negativeO ??? H O ??? HBE makes the O ??? H relation in theO ??? H—CHO group very characteristic. This alsoindicates that the interatomic distance be-tween the long-range O and H atoms is notthe suitable parameter for hydrogen-bondingformation and that sometimes they repel eachother instead of bonding.

With the results of this work, we may concludethat the localized analysis between O and H issimple, powerful, and reliable. It is our hope toapply this method to various molecular systems inthe future for any intramolecular O ??? H relation-ship determination.

ACKNOWLEDGMENTS

The authors would like to thank the NationalScience Council of the Republic of China for finan-cial support of this work under Contract No. NSC-87-2113-M-014-001. The calculation facility wasprovided by the National Center for Highperfor-mance Computing.

References

Ž1. Chen, C.; Chang, C. W.; Wang, Y. M. J Mol Struct Theo-.Chem 1994, 311, 19.

2. Chen, C.; Yih, S. C.; Sun, K. C. Chemistry; Chinese Chemi-Ž .cal Society: Taiwan, 1995; 53 1 , 35.

3. Chen, C.; Yih, S. C.; Sun, K. C. J Chung-Cheng Inst TechŽ .1996, 24 2 , 191.

4. Chang, S. C.; Chen, C. Soc Exp Prop ROC 1992, 8, 25.Ž .5. Chen, S. J.; Chen, C. Chemistry 1997, 55 2 , 19.

6. Chen, S. C. Master’s Thesis, Chung-Cheng Institute of Tech-nology, 1997.

Ž .7. Chen, C.; Shyu, S. F.; Hsu, F. S. Chemistry 1998, 56 1 , 7.

8. Chen, C.; Shyu, S. F.; Hsu, F. S., submitted.

9. Chen, C.; Shyu, S. F.; Hsu, F. S., submitted.

10. Chen, C.; Shyu, S. F.; Hsu, F. S., submitted.Ž .11. Chen, C.; Hsu, F. S.; Shyu, S. F. Chemistry 1998, 56 4 , 237.

12. Schaffer, T.; Sebastian, R.; Mckinnon, D. M.; Spevack, P. W.;Cox, K. J.; Takechi, C. S. Can J Chem 1993, 71, 960.

13. Lampert, H.; Mikenda, W.; Karpfen, A. J Phys Chem A1997, 101, 2254.

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 403

CHEN, SHYU, AND HSU

14. Borisenko, K. B.; Bock, C. W.; Hargittai, I. J Phys Chem1996, 100, 7426.

15. Portalone, G.; Schultz, G.; Domenicano, A.; Hargittai, I. JChem Phys Lett 1992, 197, 482.

16. Lampert, H.; Mikenda, W.; Karpfen, A. J Phys Chem 1996,100, 7418.

17. Foresman, J. B.; Frisch, E. Exploring Chemistry with Elec-tronic Structure Methods; Gaussian, Inc.: Pittsburgh, PA,1996.

18. Chung, G.; Kwon, O.; Kwon, Y. J Phys Chem 1998, 102,2387.

19. Orttung, W. H.; Scott, G. W.; Vosooghi, D. J Mol StructŽ .TheoChem 1984, 109, 161.

20. Yoshida, H.; Matsuura, H. J Phys Chem 1998, 102, 2691.21. Elazhary, A. A.; Suter, H. U. J Phys Chem 1996, 100, 15056.22. Sim, F.; Amant, A. S.; Papai, I.; Salahub, D. R. J Am Chem

Soc 1992, 114, 4391.

23. Zuihof, H.; Dinnocenzo, P.; Reddy, A. C.; Shaik, S. J PhysChem 1996, 100, 15774.

24. Hertwig, R. H.; Koch, W. J Comput Chem 1995, 16, 576.

25. Frisch, M. J.; Truck, G. W.; Schlegel, H. B.; Gill, P. M. W.;Johnson, B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T. A.;Petersson, G. A.; Montgomery, J. A.; Raghavachari, K.;Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J. V.; Foresman,J. B.; Peng, C. Y.; Ayala, P. Y.; Wong, M. W.; Andres, J. L.;Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.;Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian 94, Revi-sion D.1; Gaussian, Inc.: Pittsburgh, PA, 1995.

26. Neiminen, J.; Rasanen, M.; Murto, J. J Phys Chem Soc 1985,32, 385.

27. Peng, C.; Schlegel, H. B.; Frisch, M. J. J Comp Chem 1995,16, 49.

28. Peng, C.; Schlegel, H. B. Israel J Chem 1993, 33, 449.

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