IC 0 0, 1 UNCLASSIFIED

Transcription

1 5 ECURITY CLASSIFIATION OF THIS PAGE a. MbPUK I,.I:IU I I Y ~ r~g, ' lb. RESTRICTIVE MARKINGS UNCLASSIFIED 2a SECURITY CLASSIFICATION AUITH ELECTE 3. DISTRIBUTION /AVAILABILITY OF RtFORT 2b. /DOWGRAD% ECLSSIFCATON HME 0 4 EDISTRIBUTION UNLIMITED 4 PERFORMING ORGANIZATION RE UMBER( 1 5. MONITORING ORGANIZATION REPORT NUMBER(S) FJSRL-JR o 6a NAME OF PERFORMING ORGANIZATONO -6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION F.J. Seiler Research Laboratory (if applicable) FJSRL/NC 6c. ADDRESS (City, State, and ZIP Code) 7b. ADDRESS (City, State, and ZIP Code) USAF Academy Colorado a NAME OF FUNDI;4G/SPONSO ING I8b OFFICE SYMBOL g PROCUREMENT INSTRUMENIT IDENTIFICATION NUMBER ORGANIZATION AF Office of (if applicable) Scientific Research (AFOSR 8c ADDRESS (City, State, and ZIP Code) 10. SOURCE OF FUNDING NUMBERS Bldg 410 PROGRAM PROJECT ITASK jworkui Bolling AFB DC ELEMENT NO NOI NO ACESION NO 61102F I 230 F TITLE (include Security Classification) Molecular Structure and Vibrational Analysis of 2,4,6-Trinitroluene and 2,4,6-Trinitrotoluene-a-d 3 12 PERSONAL AUTHOR(S) C.P. Nash, T.E.Nelson, J.J.P. Stewart and W.R. Carper 13a TYPE OF REPORT 13b TIME COVERED 14, DATE OF REPORT (Year, Month, Day) 15 PAGE COUNT Journal Article IFROM - TO - 88 November SUPPLEMENTARY NOTATION 17 COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number) L FIELD GROUP SUB-GROUP.19 ABSTRACT 'Continue on reverse if necessary and identify by block number) >he x-ray structures of 2,4,6-trinitrotoluene and 2,4,6-trinitrotoluene-a-&- have been determined at 130K. The molecular structure and vibrational spectra ar 3acltdb h MNDO-PM3 method and are in agreement with experimental results. The short intra-and intermolecular hydrogen contacts co elate with the known thermal and ionization degradation pathways of 2,4,6-trinitrotoluene.., 20 DISTRIBUTION /AVAILABILITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATION EUNCLASSFIEDUNLIMITED 0 SAME AS RPT 03 DTIC USERS UNCLASSIFIED 22a NAME OF RESPONSIBLE INDIVIDUAL 22b. TELEPHONE (include Area Code) 22c. OFFICE SYMBOL ALAN A. SHAFFER, Major, USAF (719) FJSRL/NC DO Formn 1473, JUN 86 Previous editions ar. obsolete. _SECJ IITY CLASSIFICATION OF THIS PAGE-- IC 0 0, 1 UNCLASSIFIED

2 Sprt ih- a 4 'ra. Vol 45A. No 5. pp , 19X9 t5t4 X539 9 S3) 0,00 Printed in Great Britain 1999 Prgamon Press pl Molecular structure and vibrational analysis of 2,4,6-trinitrotoluene and 2,4,6-trinitrotoluene--d 3 C. P. NASH, T. E. NELSON, J. J. P. STEWART* and W. R. CARPERt++ Department of Chemistry, University of California, Davis, CA 95616, U.S.A.; "Frank J. Seiler Research Laboratory, United States Air Force Academy, Colorado Springs. CO 80840, U.S.A. and 'Department of Chemistry, Wichita State University. Wichita, KS 67208, U.S.A. (Received 18 October 1988; in finalform 23 November 1988; accepted 25 Norember 1988) Abstract The X-ray structures of 24,6-trinitrotoluene and 2,4,6-trinitrotoluene-a-d 3 have been determined at 130 K. The molecular structure and vibrational spectra are calculated by the MNDO-PM3 method, and are in agreement with experimental results. The short intra- and intermolecular hydrogen contacts correlate with the known thermal and ionization degradation pathways of 2,4,6-trinitrotoluene. INTRODUCTION provement over those parameters used with AM I [9] and other semi-empirical methods. Typically, use of In earlier studies [1 3], the vibrational spectra of these parameters results in a significant decrease in trinitrotoluene (TNT) i;, solid, liquid, mid vapor heats of formation errors [6]. All ground state geophase, have been compared with vibration frequencies metries were optimized using the BFGS function calculated by using semi-empirical quantum mechan- minimization procedure [10-13]. The Hessian matrix ical models. The structures predicted theoretically for the normal coordinate analysis was calculated as were in reasonable agreement with that found in a described previously [I]. room temperature X-ray diffraction study [4] for the average of the two independent molecules (designated forms A and B both here and in Ref. [4]) in the unit RESULTS AND DISCUSSION cell. The experimental structures, however, showed The heavy atom bond distances and bond angles unreasonably large variations in both the C-C obtained from the low temperature X-ray structures of ( A) and C- N ( A) bond dis- 2.4,6-trinitrotoluene and 2,4,6-trinitrotoluene-2-d,. tances, which prompted the low temperature (130 K) and the corresponding dimensions of TNT calculated redetermination of the crystal structure which we now by the M NDO-PM 3 method are given in Tables I and report. We have also determined the structure of 2. The estimated standard deviations of the heavy- TNT-,-d 3 at 130 K to obtain additional verification atom dimensions are: angles 0.4 (TNT) or on the short inter- and intramolecular hydrogen con- (TNT-d 3 ); C -C bonds A (TNT) or A tacts (potential hydrogen bonds) that were reported in (TNT-d 3 ); C-N and N-O bonds A (TNT) the previous study [4]. Finally, we have recalculated or A (TNT-d 3 (. both the predicted molecular structure and the predic- In general, the bond distances found in the present ted gas-phase vibration spectrum using the MNDO- low temperature studies are in better agreement with PM3 [5, 6] method. those calculated by the MNDO-PM3 method than are the corresponding distances obtained in the pre- EXPERIMENTAL vious room temperature structure determination (4]. The synthesis of 2,4,6-trinitrotoluene and 2,4,6-trinitrotol- The ring C-C bond distances span a much narrower uene--d 3 have been described elsewhere [7]. Crystals of each range in the low temperature structures and the C-N compound suitable for X-ray analysis were cut from larger bond distances are also closely similar. ones grown by the slow evaporation of solutions of the The dihedral angles between the ring planes and the compounds in n-propanol (TNT) or n.propanol-od (TNT- nitro groups differ by only a few degrees from those d 3 ). Data were collected at 130 K on a low temperature- found in the earlier study, as shown in Table 3. The accessorized Syntex P2 1 diffractometer. oxygen atoms on the o-nitro groups that are nearest THEORETICAL the methyl group lie on the same side of the ring plane. In the calculated structure (gas phase) the 4-nitro The calculations were accomplished with the group is almost coplanar with the phenyl ring, stabil- MOPAC program [8] using the MNDO-PM3 ized by hydrogen interactions as shown in Fig. I, while method [5, 6]. The MNDO-PM3 method uses opti- those in the 2- and 6-positions are significantly twisted mized parameters that represent a considerable im- out of this plane. The present study confirms the existence of the various short intra- and intermolecular hydrogen t Author to whom correspondence should be addressed. contacts (hydrogen bonds?) identified in the earlier 585

3 586 C. P. NASH el al. Table 1. Bond distances (A) and bond angles (degrees) for form A TNT and TNT-d, TNT TNT-d, TNT TNT-d, Distance* Obs. Calc. Obs. Angle Obs. Catc. Obs. CI-C CI -C2--C C2-C C2-C3-C C3-C C3-C4-CS C4--C C4-,CS-C CS-C CS-C6- C C6-C C6-C7-C C7-C C7 C2 C C3-N C2 C3 NI t9.9 C5-N C4-C3 NI C7-N C2 C7 N3 I (N 0)_ ) (9) C6 C7 N C44t5- N C6, C5 N (C -N 0), 117.5(6) (9) (0- N 0), 125.0( (3) *Atom designations as in Ref. (4]. Table 2. Bond distances (A) and bond angles (degrees) for form B TNT and TNT-d3 TNT TNT-d, TNT TNT-d, Distance* Obs. Calc. Obs. Angle Obs. Calc. Obs. C8-C C8-C9-CIO C9_0CI C9C IO0-C I CIO-CII CIO-CII-C ClI -Cl CII C C12-C C13-C C I3-C 14-C C 14-C C14-C9-CIO C I -N C9-CIO-N C12-NS CI I -CIO.-N Cl4-N ('9-C14-N (N08c 1.228(4) () C14-C12-N Cll--C12 N N *Atom designation as in Ref. [4]. (0-N-O) (4) (8) Table 3. Dihedral angles (degrees) between nitro groups and It, 2 03, the plant of the ring in 2,4.6-trinitrotoluene isotopomers Molecular Nitro group C7C form N 2- N A (Ref. [4]) SI C A (this work) A-d 3 (this work) '0 B (Ref. [4]) B (this work) B-d 3 (this work) Fig. I. Calculated molecular structure of 2.4,6-trinitrotol- Calc. (this work) uene. The atom designation is that of TNT structure Ain Ref. [4]. and distances are in A. work. We observe 0.. H hydrogen contacts be- hydrogen-to-nitro-oxygen interaction that has been tween two A molecules (05 H2) and an A and a B implicated in the thermal degradation of TNT. molecule (04 HI0)that approximate distances of 2.5 A. Of greater significance is the complete lack of hy- Only the first of these involves the kind of miethyl- drogen bonding involving the para-nitro groups. Such

4 2,4,6-TNT and 2,4,6-TNT-2-d absences are consistent with the para-nitro group In correlating calculated vibrational frequencies to being unreactive in the thermal or ionization break- those observed, emphasis was placed on absorption down of TNT [14-16]. intensities and isotopic substitution [3]. In the major- Tables 4 and 5 contain the calculated [5, 6] and ity of cases, calculated absorption frequencies with observed [1, 3] vibration frequencies of TNT and large transition dipoles were identified with the more TNT-d 3.The symmetry designations [1] are based on intense absorption bands. The major improvement in the nominal C,, symmetry of the calculated structure, with the principal axis in the z-direction and the.vthe calculations occurs in the NO 2 v, and V.,y, stretching frequencies, where the error compared to direction orthogonal to the plane of the ring. The A2 previous calculations [3] decreases from 34% to 22%. and B, vibrations are out-of-plane; A 2 vibrations are The C-H stretching frequencies in the i.r. inactive if the molecule has genuine C2. symmetry, cm- ' range are reproduced with an averbut such is not the case in the present instance and at age error of 1.3% vs 3.0% using the AM I method. The least some of the A,-species vibrations may become remaining frequencies over the range of observable cm -' are reproduced with an average error Table 4. Observed and calculated frequencies (cm- ') for 2.4,6-trinitrotoluene Transition KBr Vapour ",1, Symmetry Assignmenrtt dipole B, B 2 11, B, B, h B, A, A, , A, B B, B , , A, B Accesion For , A B, ,30 NTIS C/-A&I B, 4, OTIC TAB Il Unannounced J , 123( B, 10, 12 0, A) B, 9 0,05 0,19 JUSfCdtiOn A, A, 19 5 By B2 19 5,90 Oistribution A, B, Avallablily Cotlts , 9, , , 7, II Avail and Of Dist S,eC Id B, , A, 8, , A-, B2 I A, I B A, A, *Data from Ref. [1, 3]. t Assignments of vibrational frequencies: I. Ring C-H stretch; 2. Methyl C-H asym. stretch; 3. Methyl C-H sym. stretch; 4. Methyl H-C-H asym. bend; 5. Methyl H-C-H sym. bend; 6. Methyl rock; 7. Methyl umbrella; 8. C-C stretch: methyl to ring; 9 C-C ring stretch: In King i-c-c in plane bcnd; 11. Methyl ag Ct.C in-plane bend; 12. Ring CCC bend; 13. Out-of-plane bend of ring H; 14. Out-of-plane bend of methyl C; 15. C-N bend; 16. C-N stretch; 17. C-N-O bend; 18. NO 2 asym. stretch; 19. NO 2 sym. stretch.

5 588 C. P. NASH et al. Table 5. Observed and calculated frequencies (cm- ) for 2,4,6-trinitrotoluene-y-d 3 V.'*, Transition KBr Vapour 1, Symmetry Assignmentt dipole 457, B, B, B A, 5, B B, A 2, B A A, A B, A, B , B, 12 0, A B, A B, B, B, , , A A B, A B B A A A, B B, A, B, , B, B A, B, , , I 0.42 *Data from Refs [I. 3]. t Assignments of vibrational frequencies. See Table 4. ofless than 21 cm-', down slightly from the 24 cm [3J W. R. CARPER and J. P. STEWART, Spectrochim Acta with the AMI method [3].* 43A, 1249 (1987). [4] W. R. CARPER, L. P. DAVIS and M. W. EXTINE, J. ph).%. Acknowledgements -The authors wish to thank H. HOPE, in Chem. 86, 459 (1982). whose laboratory the X-ray work was done. W. R. C. wishes [5] J. i. P. STEWART, J. comp. (hem. 0, 209 ( to acknowledge the NRC for fellowships and the generous [6] J. J. P. STFWART. J. omp. ('hem. 10, 221 (1989). support of the Frank 1. Seiler Research Laboratory. [7] R. C. DOREY and W. R. CARPFR, J. Chem. Enq. Data (1984). REFERENCES [8] J. J. P. STEWART. MOPAC, Quantum Chemistry Prog. Exch. No. 455 (1983). [1] J. 1. P. STEWART, S. R. Bosco and W. R. CARPER, [9] M. J. S. DEWAR, E. G. ZOEBISCH, E. F. HEALY and Spectrodhim. Acta 42A, 13 (1986). J, J " P. STEWART, J. Am. chem. Soc (1985). [2] W. R. CARPER, S. R. Bosco and J. J. P. STEWART, [10] C. G. BROYDEN, J. Inst. Math. App. 6, 222 (1970). Spectrochim. Acta 42A, 461 (1986). [II] R. FLETCHER, Camp. J. 13, 317 (1980). [12] D. GOLDFARB, Math. Comput. 24, 23 (1970). [13] D. F. SHANNO, Math. Comput. 24, 647 (1970). *Tables of positional and thermal parameters and struc- [14] T. M. McKINNEY, L. F. WARREN, 1. B. GOLDBERG and ture factors are available from the Directory of the Cam- J. T. SWANSON, J. phys. Chem. 90, 1008 (1986). bridge Crystallographic Data Centre I nivermity Chemical [15 1J. T. SWANSON, L. P DAVIS. R. C. DOPFY and W. R. Labuiatory, Lensfield Road, Cambridge CB2 IEW, U.K. CARPER, Magn. Reson. Chem. 24, 762 (1986). The request should be accompanied by the full literature [16] W. R. CARPER, R. C. DOREV, K. B. TOMER and F. W. citations for this report. CRow, Org. Mass Spectrom (1984).