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MOLECULAR STRUCTURE ELSEVIER

Journal of Molecular Structure 440 (1998) 227-235

Ab initio quantum chemical and NMR study of the symmetric monooximes of 1,2,3-phenalenetrione and 1,2,3-indantrione Venelin Enchev a'*, Galya Ivanova a, Angel Ugrinov a, Georgi D. Neykov h, Stoyan Minchev c, Neyko Stoyanov d alnstitute of Organic Chemistry, Bulgarian Academy of Sciences, Acad G Bonchev Str., 1113 Sofia, Bulgaria blnstitute for Foreign Students, 1113 Sofia, Bulgaria "Department of Chemistry, Varna University of Economics, 77 Knjaz Boris I Str., 9002 Varna, Bulgaria dlnstitute of Chemical Technology and Biotechnology, 3 Aprilsko vastanie Blvd., 7200 Razgrad, Bulgaria

Received 15 April 1997; revised 11 June 1997; accepted 16 June 1997

Abstract

The possibility for nitroso-oxime tautomerism in symmetric monooximes of 1,2,3-phenalenetrione and 1,2,3-indantrione is studied by means of ab initio quantum chemical methods and NMR spectroscopy. For both compounds, ab initio calculations with different basis sets predict the oxime tautomer as most stable in agreement with the JH- and 13C-NMR results in CDC13 and DMSO-d6 solutions. A coalescence of the signals for the carbon atoms from carbonyl groups of 1,2,3-phenalenetrione monooxime in DMSO-d6 solution at temperature 360 K is observed. This coalescence may be attributed to rotation of the hydrogen atom from the hydroxyl group around the N - O bond. The rotational transition structures for both compounds at different computational levels were located in the gas phase and in solution. © 1998 Elsevier Science B.V. Keywords: Monooxime; Ab initio; NMR; Structure; Rotation barrier

1. Introduction Tautomeric equilibria of the monooximes of benzoquinone (nitrosophenol) and naphthoquinone (nitrosonaphthol) are well investigated and they depend on the kind of solvent used [1]. The data for the structure and tautomerism of 2-nitroso substituted cyclic 1,3-diones are scarce despite their practical applications. For example, colored activated esters obtained upon interaction of N-protected amino acids with 2-hydroxyimino-l,3-indandione [2] can react with amines and esters of aminoacids [3] forming * Corresponding author. E-mail: [email protected]

peptides. W e investigated the tautomerism and structure of 2-hydroxyimino-l,3-indandione both experimentally (IR and U V - V i s spectroscopy) [4] and theoretically ( M N D O and A M 1 ) [4,5]. Recently Mitewa et al. [6] reported results on the complexation of the symmetric monooxime of 1,2,3-phenalenetrione with Co(II), Ni(II) and Cu(II). However, the structure of the ligand has not been discussed. The aim of the present paper is to investigate the structure of the symmetric monooximes of 1,2,3-phenalenetrione and 1,2,3-indantrione in gas phase and in solution. The effect of solution is calculated by the Onsager reaction field model as implemented in the context of ab initio M O theory. This method has

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228

V. Enchev et al./Journal of Molecular Structure 440 (1998) 227-235

been applied successfully to study several solvent effect problems [7-12]. The tautomeric equilibrium in CDC13 and DMSO-d6 solutions is studied experimentally by means of ~H- and ~3C-NMR spectroscopy.

in DMSO-d6 at higher temperatures were measured (from 300 K to 360 K). The following standard Bruker library pulse programs were used: zg, dept, cosy and hxco. Standard 1D experiments with 30 ° pulses, 1 s relaxation delays, 16 K time domain points, zerofilled to 64 K for the protons and 32 K for the carbons were performed. Hard pulses with 90 ° pulse widths of 11 /~s for the protons and 6 #s for the carbons at a power level of 3 dB below the maximum output were used. The distortionles enhancement by polarisation transfer (DEPT) spectra were obtained under the same conditions as the ~3C-NMR spectra, and ~-= (2 'JCH) -1 = 3.45 /zs was used. The 2D experiments were typically performed with a relaxation delay 2 s; 1 K data points in F2 and 256 data points in F1 for the homonuclear( IH/IH correlation spectroscopy, COSY), and 64 for the heteronuclear ('H/'3C correlation spectroscopy, HETCOR) experiments were acquired.

2. Experimental The symmetric monooximes of 1,2,3-indantrione and 1,2,3-phenalenetrione were synthesized according to Refs. [13,6] respectively. The second compound was obtained [6] with higher yield 80-85% instead of 65% [14]. The reaction occurs in dioxane instead of THF. The reaction mixture was poured on ice and the resulting product was with higher purity (M.p. is 172-170°C [6] instead of 160-170°C [14]). 2.1. NMR spectroscopy

2.2. Quantum-chemical calculations The NMR spectra were measured using a dual 5 mm probe head on a Bruker Avance DRX-250 spectrometer, operating at 250.13 and 62.90 MHz for ~H and 13C, respectively, with TMS as standard. NMR spectra in CDC13 and DMSO-d6 were recorded at ambient temperature (300 K). Also 13C-NMR spectra 16

17

H

H

H

0

The structure optimizations for the monooximes of 1,2,3-phenalenetrione 1 and 1,2,3-indantrione 2 molecules in their different tautomeric forms (Fig. 1) were performed without any geometrical restrictions by using the SCF procedure with split-valence basis

H

H

H

H

0 ~H

q o /

~

22

H

21

20

1A

1B

12

10

15

11

H

2A

O

18

H

IC o~H

H

2B

H

O

2C

Fig. 1. 'Oxime' A, 'enol' B, and 'oxo' C tautomeric forms of 1,2,3-phenalenetrione monooxime 1 and 1,2,3-indantrione monooxime 2.


Fig. 2. Calculated ab initio 6-31G(d,p) 'closed' A and 'open' Al rotamers for oxime tautomer of 1 and 2. set 3-21G and 3-21G(p) (plus polarization functions on hydrogen atoms) with the 6AMESS program [15]. Finally, a full optimization for tautomers A and B (Fig. 1) and rotamer AI (Fig. 2) of both compounds were carried out at 6-31G(d,p) level. The rotational transition-state searching was performed using the algorithms [16] which form the 'standard method' for 6AMESS geometry searches. The gradient optimizations were terminated when the gradient length over all optimized parameters was reduced down to 0.0001 Hartree Bohr -l. All the structures were characterized by computing harmonic frequencies, which are used also to compute zero-point energies (ZPEs). Frequency calculations at the equilibrium geometries yielded only real frequencies and hence all structures correspond to local minima. Frequency calculations were also carried out for the transition states and these stationary points were confirmed to be true transition state by having only one imaginary frequency. All the hessians were calculated numerically with the 3-21G(p) basis set to economize computer time [17]. To obtain the true energy a zero-point energy correction was added to the total energy for each species. The free energy was calculated by using standard statistic-mechanical formulae as implemented in GAMESS.The calculated gas-phase free energies are given relative to the most stable tautomer, i.e. A, for three temperatures (300, 330 and 360 K).

229

For the simulation of a polar environment the Onsager self-consistent reaction field (SCRF) model [18,19] was used as implemented in 6AMESS. Only the electrostatic effects of solvation are included in the Onsager model and other forces such a cavity work, dispersion or exchange repulsion effects are neglected (for a general description of solvation energies see Ref. [20]). In Onsager reaction field theory the solvent is considered as a uniform dielectric with a given dielectric constant e. The solute is situated in a spherical cavity of a radius a0 in the solvent medium. The permanent dipole of the solute then induces a dipole (reaction field) in the surrounding medium, which in turn will interact with the solute's dipole and this solute-solvent interaction is updated until self-consistency is achieved. The cavity radius a0 is estimate from the greatest dimension at the molecule. The diameter of the molecule is calculated from the greatest internuclear distance and adding the Van der Waals radii [21] of the atoms involved. This cavity radius was then kept fixed for both conformers and transition state investigated.

3. Results and discussion The compounds studied, 1 and 2, may exist in three tautomeric forms, 'oxime' A, 'enol' B, and 'oxo' C, shown in Fig. 1. A stable rotamer of the tautomer A for both compounds in which the OH group is not in a favorable position for hydrogen bonding is also found by the ab initio calculations. We note this 'open' rotamer as A1 (Fig. 2). The calculated relative and total energies in the gas phase and DMSO solution are given in Table 1 and Table 2. The differences in the energies for the species studied are listed in Table 1 for a series of basis sets. Single point calculations based on optimized 3-21G(p) geometries are performed at the 6-31G(d,p) level for all species considered to show the effect of basis set quality on the relative stability and barriers. All ab initio calculations predict the oxime tautomer A for both compounds as most stable (Table l). The 'open' rotamer A l has a higher energy than the 'closed' hydrogenbonded rotamer for compounds 1 and 2. Experimental NMR measurements in solutions of CDCI3 and DMSO-d6 identify the oxime tautomer only. The 13C-NMR chemical shifts measured at room

230


Table 1 Calculated relative stabilities (in kcal rnol -~) for tautomers A, B and C of 1,2,3-phenalenetrione monooxime and 1,2,3-indantrione monooxime (Fig. 1), rotamer Ai (Fig. 2) and barrier of rotation TS(A ~ A0, (Fig. 3Fig. 4). Tautomers Computational level 1,2,3 -phenalenetrione monooxime 3-21 G//3-21G 3-21G(p)//3-21G(p) 6-31 (d,p)G//3-21G(p) 6-31 (d,p)/G/6-31G(d,p) SCRF/6-31G(d,p)//6-31G(d,p) a 6-31 (d,p)//6-31G(d,p) + 0.893 xAZPE/3-21G(p) AG300 b AG330 b AG360 b 1,2,3-indantrione monooxime 3-21 G//3-21G 3-21G(p)//3-21G(p) 6-31G(d,p)//3-21G(p) 6-31G(d,p)//6-31G(d,p) SCRF/6-31(d,p)//6-31G(d,p) c 6-31G(d,p)//6-31G(d,p) + 0.893xAZPE/3-21G(p) AG30O b AG330 b AG360 b

Transition state TS(A -.-. A~)

A

A~

B

C

0.00 0.00 0.00 0.00 0.130 0.00 0.00 0.00 0.00

4.87 5.18 4.51 4.61 6.36 4.23 3.32 3.24 3.16

10.83 12.24 7.42 7.86 7.71 7.14

29.66 37.11 16.38

12.00 12.31 12.68 12.11 13.05 10.56 8.57 8.53 8.49

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.52 0.96 1.36 1.40 2.91 1.02 0.34 0.29 0.25

19.78 20.98 14.79 14.94 14.88 14.22

27.85 34.74 15.14

8.62 8.80 10.61 10.94 11.74

9.70 7.35 7.32 7.30

a SCRF in DMSO, a0 = 5.79 A.. b AGr = AE + AZPE + AH - TAS. c SCRF in DMSO, a0 = 5.53 ,~. t e m p e r a t u r e for c o m p o u n d 2 in C D C I 3 a n d D M S O - d 6 at 185.5 p p m a n d 180.0 p p m w e r e a s s i g n e d to a t o m s C - 7 a n d C - 9 for t a u t o m e r A (Fig. 1). N o s o l v e n t d e p e n d e n c e o f c h e m i c a l shifts for this c o m p o u n d was observed. The 13C-NMR c h e m i c a l shifts m e a s u r e d for c o m p o u n d 1 in s o l v e n t s CDC13 a n d D M S O - d 6 at r o o m t e m p e r a t u r e 3 0 0 K are p r e s e n t e d in T a b l e 3. T h e 13C-NMR d a t a in D M S O - d 6 at h i g h e r t e m p e r a t u r e s are also i n v o l v e d . T h e c h e m i c a l shifts at 183.6 a n d 179.1 p p m in CDC13 a n d 181.1 a n d 177.5 p p m in D M S O - d 6 at r o o m t e m p e r a t u r e w e r e a s s i g n e d to a t o m s C - 2 a n d C - 4 for t a u t o m e r I A (see Fig. 1 a n d T a b l e 3). A c o a l e s c e n c e o f the signals for t h e s e a t o m s in D M S O - d 6 s o l u t i o n at t e m p e r a t u r e 3 6 0 K ( T a b l e 3) w a s o b s e r v e d . W e a t t r i b u t e that this c o a l e s c e n c e to r o t a t i o n o f h y d r o g e n a t o m f r o m h y d r o x y l g r o u p a r o u n d the N - O b o n d . T h e r o t a t i o n b a r r i e r s a r o u n d N - O b o n d in c o m p o u n d s 1 a n d 2 (Fig. 2) w e r e s t u d i e d t h e o r e t i c a l l y in the gas p h a s e a n d in D M S O s o l u t i o n v i a a b initio c a l c u l a t i o n s . T h e c a l c u l a t e d e n e r g i e s for b o t h r o t a m e r s a n d t h e i r

Fig. 3. Calculated ab initio 6-31G(d,p) transition state for the process of rotation for compound 1.


231

Table 2 Calculated total energies and ZPE (in a.u.) of tautomer A, its rotamer A1 and barrier of rotation T S ( A ~ A I ) for 1,2,3-phenalenetrione m o n o o x i m e and 1,2,3-indantrione m o n o o x i m e in the gas phase (e = l ) and in D M S O (e = 46.68). Calculated values of the dipole m o m e n t in solution are given in parentheses. H is in kcal mol-L and S in cal K -I mol -I Computational level

A

1,2,3 -phenalenetrione m o n o o x i m e 3-21G//3-21G 3-21G(p)//3-21G(p) 6-31G(d,p)//3-21G(p) 6-31G(d,p)//6-31G(d,p) SCRF/6-31G(d,p)//6-31G(d,p) a ZPE/3-21G(p) H 300 S 330

-

Dipole m o m e n t b

1,2,3-indantrione

771.011638 771.062149 775.364160 775.370890 775.374690 0.189111 126.028 102.849

AI

TS(A ~ A ~)

-

-

771.003877 771.053892 775.356741 775.363545 775.364556 0.188440 125.858 105.339

7.46 (8.91) a

3.84 (4.60) a

770.992511 771.042532 775.343946 775.351594 775.353899 0.186347 124.435 104.183 5.90 (6.83) a

monooxime

3-21G//3-21G 3-21G(p)//3-21G(p) 6-31(d,p)//3-21G(p) 6-31 (d,p)//6-31G(d,p) SCRF/6-31 (d,p)//6-31G(d,p) c ZPE/3-21G(p) H3°° S 330 Dipole m o m e n t b

-

619.206683 619.245760 622.703082 622.709362 622.712332 0.137063 92.158 93.210

-

619.205848 619.244224 622.700922 622.707126 622.707000 0.136379 91.933 94.713

6.24 (7.25) c

-

2.73 (3.20) c

619.192946 619.231735 622.686169 622.691922 622.694050 0.134850 90.056 95.036 5.32 (6.09) ¢

a SCRF calculations in D M S O with a0 = 5.79 ,~. b 6-3 lG(d,p)//6-31G(d,p) values in D. c SCRF calculations in D M S O with a0 = 5.53 ,~.

Table 3 ~3C-NMR chemical shifts (in ppm) for 2-hydroxyiminophenalene-1,3-dione in solvents CDCI3 and DMSO-d6. For numbering of atoms see Fig. 1 Atoms

CDC13 (300 K)

DMSO (300 K)

DMSO (330 K)

DMSO (360 K)

2 4 3 10 7 8 13 12 14 9 6 11 15

183.6 179.1 146.6 137.4 135.5 132.8 131.2 130.9 125.6 125.6 127.4 126.9

181.1 177.5 147.6 134.9 134.9 132.7 130.2 129.2 128.8 128.3 128.3 127.3 127.3

180.0 178.5 147.1 134.8 134.8 132.6 130.1 128.7 128.7 128.2 128.2 126.8 126.8

178.9 178.9 146.8 134.5 134.5 132.9 130.8 128.3 128.3 128.2 128.2 126.4 126.4


232

Table 4 A b initio 3-21G(p) a n d 6-31G(d,p) calculated structural parameters for the both rotamers 1A and 1A l of 2 - h y d r o x y i m i n o p h e n a l e n e - 1 , 3 - d i o n e (Fig. 2) in the gas phase a n d in solvent D M S O . B o n d lengths are given in a n g s t r o m s and b o n d angles in degrees. F o r n u m b e r i n g of a t o m s see Fig. 1. The torsional angles are not given because both rotamers was f o u n d to be planar Parameter

1A

1A t

3-21G(p) Bonds O1 - C 2 C2-C3 C2-C9 C3-C4 C3-N5 C4-C6 C4-022 N5-O23 C6-C7 C6-C8 C 7 - C 15 C8-C9 C 8 - C 13 C 9 - C 10 C10-CI 1 C 11 - C 12 C12-C13 C13-C14 C 1 4 - C 15 C 1 0 - H 16 C 11 - H 17 C 1 2 - H 18 C 1 4 - H 19 C 15-H20 C7-H21 O1-H24 O23-H24 O1-O23 B o n d angles C3-C2-O1 C4-C3-C2 N5-C3-C2 C6-C4-C3 C6-C7-C15 C7-C6-C4 C7-C15-C14 C8-C6-C4 C9-C2-C3 C9-C8-C6 C10-C9-C2 C 10-C9-C8 C 11 - C 1 0 - C 9 C12-C1 I-C10 C13-C12-C11 C13-C8-C6 C14-C13-C12 C14-C13-C8

1.231 1.478 1.464 1.493 1.279 1.480 1.212 1.386 1.363 1.414 1.408 1.416 1.407 1.365 1.406 1.362 1.417 1.417 1.360 1.069 1.069 1.071 1.071 1.069 1.069 1.717 0.955 2.553

120.5 121.1 124.0 116.5 120.9 118.3 119.9 121.6 118.0 121.9 118.5 120.6 120.7 119.8 121.0 119.2 121.9 119.1

6-31G(d,p)

6-31G(d,p) a

1.209 1.491 1.478 1.504 1.275 1.490 1.192 1.309 1.366 1.422 1.409 1.424 1.410 1.368 1.407 1.361 1.418 1.418 1.360 1.074 1.074 1.076 1.076 1.075 1.074 1.743 0.958 2.576

0.001 0.003 0.005 0.004 0.002 0.003 0.001 0.005 0.001 0.000 0.001 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.017 0.001 0.011

120.6 121.1 124.2 116.7 121.0 118.7 119.8 121.1 117.9 122.5 118.8 120.5 120.8 119.7 121.2 118.9 121.6 119.2

-

-

-

-

- 0.4 - 0.1 0.0 - 0.1 0.1 0.1 0.0 0.0 0.0 0.2 0.1 0.0 0.1 - 0.1 0.1 - 0.1 - 0.2 0.1

3-21G(p)

1.214

1.495 1.482 1.506 1.266 1.476 1.213 1.408 1.363 1.414

1.407 1.414

1.409 1.363 1.408 1.360 1.417 .417 .361 .068 .069 .071 .071 .069 .069 3.509 0.942 2.580

123.0 121.0 126.0 117.1 120.8 118.1 119.8 121.5 116.5 121.8 117.8 120.2 120.9 119.9 120.8 119.0 121.8 119.1

6-31G(d,p)

1.192 1.508 .491 .513 .264 .489 .192 .326 .366 .422 1.408 1.423 1.411 1.366 1.409 1.360 1.418 1.417 1.360 1.073 1.075 1.076 1.076 1.075 1.074 3.525 0.945 2.598

122.2 120.9 126.0 117.2 120.9 118.6 119.8 121.1 116.7 122.5 118.2 120.2 121.0 119.8 121.0 118.7 121.5 119.2

6-31G(d,p) a

0.001 0.002 - 0.002 0.001 0.000 - 0.003 0.001 0.003 0.001 0.000 0.000 0.000 0.000 0.001 -

0.001

0.000 0.000 0.001 0.000 0.000 -

0.001

0.000 0.000 0.000 0.000 - 0.003 - 0.001 - 0.003

- 0.2 0.0 0.0 0.0 0.1 0.0 - 0.1 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0

233


Table 4 (Continued) Parameter

3-21G(p) C15-C14-C13 H 16-C 10-C9 H17-CI I-C10 H 18-C 12-C 11 H19-C14-C13 H20-C 15-C 14 H21-C7-C6 O22-C4-C3 O23-N5-C3 H24-O23-N5

1A1

1A

120.7 118.7 119.6 120.3 118.8 120.5 118.4 122.2 120.5 109.2

6-3 lG(d,p) 120.9 118.8 119.7 120.1 118.7 120.5 118.5 121.8 121.1 110.6

6-31G(d,p)a 0.0 0.0 0.1 0.0 0.0 0.0 0.0 - 0.4 - 0.2 - 0.4

3-21G(p)

6-31G(d,p)

120.8 118.4 119.6 120.5 118.7 120.5 118.5 121.4 116.6 102.6

121.0 118.6 119.6 120.3 118.7 120.5 118.6 121.2 117.8 104.3

6-31G(d,p)~ 0.0 0.0 0.1 0.0 0.0 0.0 0.0 - 0.2 0.0 - 0.2

Change from the gas phase to solution. rotational transition states of the compounds studied are given in Table 2. The ab initio calculated barrier is fairly invariant ( < 0.7 kcal moi -I) to the basis sets for compound 1 (Table 1). A stronger effect arises when zero-point energy correction is included into the total energies. Calculations at the 6-31G(d,p) level after including ZPE correction scaled by 0.893 [22] give 10.56 and 9.70 kcal mol -I barrier the oximes for 1 and 2 respectively. The calculated free energy rotational barriers at 300 K for compounds 1 and 2 are 8.57 and 7.35 kcal mo1-1 respectively. There is a tendency for lowering of the barrier with increasing temperature (Table 1). The calculated higher rotational barrier for the oxime tautomer of compound 1 could be explained with intramolecular hydrogen bonding. A b initio calculations at the 6-31G(d,p) level predict the O1...O23 distance for 1A (Fig. 1) to be 2.576 A (Table 4) while the O10...O17 distance for 2A (Fig. 1) is calculated to be 2.769 ,~ (Table 5), i.e. in the last case there is no intramolecular hydrogen bond. Our theoretical data are in agreement with the previous study [4] on compound 2 in CHC13 solution, indicating that there is no formation of an intramolecular hydrogen bond. The calculated total energies in the gas phase and D M S O solution for the rotamers A and A l of both compounds are presented in Table 2. The overall solvent effect is reflected by the values of dipole moments. As seen in Table 2 the calculated dipole moments at 6-31G(d,p) level of the 'closed' rotamers A (Fig. 2) are larger than those of the corresponding 'open' rotamers A t by about 3.6 D in the gas phase and 4.3 D in D M S O solution. Thus one would expect

a different solvent stabilization in polar solution. This effect is clearly pronounced in a polar medium of D M S O (Table 1). It was calculated that the barriers increased in D M S O (Table 1), as a result of the greater stabilization of the more polar ground state, compared to the less polar transition state (Table 2). Since the ground state has a large dipole moment, the difference in D M S O between the ground and transition state is greater with 0.94 kcal mol -l for 1 than 0.8 kcal mol -l for 2, leading to the greater solvent effect. The geometrical parameters of the A tautomer and its rotamer A 1 for compounds 1 and 2 in the gas phase and the relative changes observed in D M S O environment are reported in Tables 4 and 5. In the ab initio calculations the geometries are found to be planar. As can be seen from Tables 4 and 5, the geometrical parameters computed at the 3-21G(p) and 6-31G(d,p) levels are almost the same. The only appreciable differences concern the lengths of the N - O and C - O

i ~

~

-,

Fig. 4. Calculated ab initio 6-31G(d,p) transition state for the process of rotation for compound 2.


234

Table 5 A b initio 3-21G(p) a n d 6-31G(d,p) calculated structural parameters for both the rotamers 2 A and 2 A 1 o f 2 - h y d r o x y i m i n o - 1,3-indandione (Fig. 2) in the gas p h a s e and in solvent D M S O . B o n d lengths are given in a n g s t r o m s and b o n d angles in degrees. F o r n u m b e r i n g o f a t o m s see Fig. 1. The torsional angles are not given because both rotamers were found to be p l a n a r P~ameter

2A

2A1

3-21G(p) Bonds C 1- C 2 C2-C3 C3-C4 C4-C5 C1 - C 6 C4-C7 C5-C6 C5-C9 C7-C8 C8 - C 9 C 7 - C 10 C 8 - N 16 C9-O11 N 16-O17 C3 - H 12 C 2 - H 13 C 1- H 14 C 6 - H 15 O 17 - H 18 O10-H18 O17-O10 B o n d angles C3-C2-C 1 C4-C3-C2 C5-C4-C3 C5-C6-C1 C6-C1-C2 C6-C5-C4 C7-C4-C3 C8-C7-C4 C8-C9-C5 C9-C5-C6 C9-C8-C7 O 10-C7-C4 O11 - C 9 - C 5 H12-C3-C2 H13-C2-CI H14-C1-C2 H 15-C6-C 1 N16-C8-C7 O17-N16-C8 HI8-OI7-N16

6-31G(d,p)

6-31G(d,p) a

1.395 1.383 1.385 1.388 1.384 1.481 1.383 1.494 1.494 1.501 1.198 1.262 1.186 1.324 1.074 1.075 1.075 1.074 0.955 1.947 2.769

0.000 0.001 0.000 0.002 0.001 0.002 0.000 0.002 0.003 0.001 0.000 0.001 0.000 0.004 0.000 0.000 0.000 0.000 0.000 0.017 0.012

1.391 1.388 1.377 1.385 1.389 1.473 1.375 1.489 1.487 1.495 1.218 1.264 1.205 1.404 1.069 1.069 1.070 1.069 0.952 1.894 2.724

120.7 117.7 121.5 117.9 121.0 121.1 128.5 106.1 104.7 128.0 108.3 128.5 126.9 121.5 119.5 119.3 121.5 128.3 117.8 109.8

120.9 117.6 121.4 117.8 121.2 121.0 128.4 106.0 104.8 128.2 108.3 128.0 127.0 121.6 119.3 119.1 121.7 128.7 118.6 111.2

a C h a n g e f r o m the gas phase to solution.

-

-

-

-

-

0.0 0.1 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.1 0.5 0.4 0.1 0.0 0.0 0.1 0.0 0.2 0.3

3-21G(p)

1.392 1.387 1.377 1.381 1.387 1.485 1.377 1.481 1.503 1.504 1.206 1.256 1.206 1.419 1.069 1.070 1.070 1.069 0.941 3.725 2.796

121.8 117.9 121.3 118.3 121.1 121.3 127.6 104.8 105.1 128.1 108.5 126.3 127.4 121.6 119.4 119.4 121.6 131.2 113.6 103.2

6-31G(d,p)

6-31G(d,p) a

1.396 1.383 1.385 1.386 1.383 1.491 1.385 1.488 1.511 1.506 1.187 1.256 1.187 1.335 1.074 1.075 1.075 1.074 0.944 3.766 2.838

0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.001 0.001 0.001 0.000 0.001 0.000 0.003 0.000 0.000 0.000 0.000 0.000 0.002 0.003

121.0 117.8 121.2 117.8 121.0 121.2 127.7 104.8 105.4 128.2 108.2 126.6 127.2 121.7 119.2 119.2 121.7 131.5 115.2 104.9

-

-

-

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 - 0.1 0.2 0.2 0.0 0.0 0.0 0.0 0.0 - 0.1 - 0.2

v. Enchev et aL/Journal of Molecular Structure 440 (1998) 227-235

b o n d s w h i c h are s h o r t e r w h e n the 6 - 3 1 G ( d , p ) b a s i s set w a s used. It w a s f o u n d that the S C R F h a s a s m a l l i n f l u e n c e o n the m o l e c u l a r g e o m e t r i e s . T h e s t r u c t u r e s o f the t r a n s i t i o n states are s h o w n in Figs. 3 a n d 4. T h e t r a n s i t i o n state for 2 A ---* 2 A ~ w a s f o u n d to b e p l a n a r only, the h y d r o g e n a t o m f r o m the h y d r o x y l g r o u p b e i n g o u t o f this p l a n e (Fig. 4). H o w e v e r it c a n b e s e e n f r o m Fig. 3 t h a t t h e r e are s u b s t a n t i a l c h a n g e s in the s i x - m e m b e r e d c y c l e i n c l u d i n g c a r b o n y l g r o u p s for t r a n s i t i o n state 1A ---* 1A~.

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235

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