Table S1: Selected bond lengths (Å), bond angles (degree), dihedral angles (degree) of geometry optimized MCAA

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Supporting Information

Theoretical Investigations on the Mechanism and Kinetics of OH Radical Initiated Reactions of Monochloroacetic Acid

R.Bhuvaneswari, L. Sandhiya and K. Senthilkumar*

Department of Physics, Bharathiar University, Coimbatore, India-641 046.

*Corresponding author: Fax No: +91-422-2422387, E-Mail: [email protected]

Table S1: Selected bond lengths (Å), bond angles (degree), dihedral angles (degree) of geometry optimized MCAA

Parameter ^#M06-2X/6-311+G(d,p) ^$MP2/6-31G** ^@Experimental

C1-C2 1.514 1.513 1.508

C1=O2 1.192 1.18 1.223

C1-O1 1.347 1.33 1.352

O1-H1 0.967 0.95 0.97

C2-Cl1 1.768 1.766 1.778

C2-H2 1.089 1.08 1.09

C2-H3 1.089 1.08 1.09

C2-C1=O2 127.3 127.4 126.1

O2=C1-O1 124 123.7 123.3

C2-C1-O1 108.8 108.9 110.6

C1-O1-H1 107.7 108.5 105.8

Cl1-C2-C1 112.3 113.3 112.5

H2-C2-C1 108.9 108.8 109.5

H3-C2-C1 108.9 108.8 109.5

C2-C1(=O2)O1 180 180 180

O2=C1-O1-H1 -0.0 0 0

Cl1-C2-C1-O1 -0.0 0 10

H2-C2-C1=O2 120.8 121.2 120

H3-C2-C1=O2 -121 -121.2 -120

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$ - Values taken from Ref[28]

@ - Experimental values taken from Ref[29]

# - Present study

Table S2: Harmonic vibrational frequencies (cm^-1) calculated at M06-2X/6-311+G(d,p) level for CH2 ClC(O)OH+OH system

System Frequencies(cm^-1)

CH2 ClC(O)OH 68, 217, 410, 492, 628, 632, 821, 924, 952, 1172, 1215, 1294, 1400, 1461, 1918, 3124, 3180, 3830

RC1 52, 71, 123, 177, 265, 388, 427, 543, 577, 658, 724, 835, 939, 950,1207, 1223,1337, 1429,1455, 1863, 3099, 3156, 3581, 3651 TS1 1469i, 37, 130, 164, 373, 394, 539, 572, 608, 663,744, 854, 948, 983,

1213, 1300, 1444, 1473, 1478, 1722, 1748, 3107, 3167, 3848

PC1 19, 723, 140, 161, 251, 282, 290, 395, 500, 556, 665, 790, 885, 935, 1116, 1222, 1316, 1452, 1617, 1823, 3105, 31756, 3816, 3968

RC2 34, 68, 69, 158, 225, 265, 390, 465, 509, 626, 633, 820, 916, 959, 1159, 1228, 1300, 1388, 1446, 1926, 3119, 3173, 3727, 3824

TS2 1234i, 37, 70, 119, 209, 220, 407, 493, 619, 644, 750, 833, 885, 938, 1098, 1173, 1197, 1281, 1410, 1452, 1898, 3171, 3763, 3843

PC2 49, 111, 149, 156, 164, 223, 344, 403, 434, 507, 582, 642, 742, 864, 1031, 11634, 1302, 1442, 1606, 1812, 3240, 38489, 3860, 3995

RC3 34, 75, 82, 127, 221, 243, 360, 409, 509, 631, 640, 8056, 923, 957, 1173, 1219, 1298, 1404, 1459, 1913, 3139, 3194, 3764, 3840

TS3 1144i, 32, 75, 124, 242, 261, 417, 434, 597, 610, 743, 752, 936, 974, 1007, 1112, 1223, 1366, 1463, 18356, 3193, 3313, 3830,3840

PC3 35, 489, 100, 115, 211, 347, 441, 561, 611, 661, 670, 769, 775, 957, 1010, 1239, 1375, 1397, 1485, 1755, 3196, 3323, 3565, 3839

OH 3766

H2O 1596, 3894, 4000 HOCl 785, 1253, 3863

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Figure S1: IRC plots for the transition states TS1, TS2 and TS3 involved in the initial reaction of MCAA with OH radical at M06-2X/6-311+G(d,p) level of theory.

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Figure S2: IRC plot for the transition states TS4 involved in the formation of peroxy radical intermediate I4 at M06-2X/6-311+G(d,p) level of theory.

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Figure S3: IRC plots for the transition states TS5 and TS6 involved in the formation of alkoxy radical intermediate and chloro-hydoxyperoxy-acetic acid product at M06-2X/6-311+G(d,p) level of theory.

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Table S3: Relative energies ∆ETot (kcal/mol) for the proposed reaction of MCAA with OH radical calculated at M06-2X, MPWB1K and CCSD(T) methods.

Stationary points

M06-2x/ cc-pVTZ MPWB1K/ cc-pVTZ CCSD(T)/ cc-pVTZ

∆ETot ∆ETot ∆ETot

R+OH 0 0 0

RC1 -10.76 -9.54 -9.74

TS1 0.67 2.38 2.28

IC1 -8.08 -5.38 -7.49

I1+H2O -1.5 -1.8 -3.8

RC2 -4.69 -3.01 -4.09

TS2 2.14 4.24 3.65

IC2 -31.53 -27.76 -29.3

I2+ H2O -25.68 -23.76 -24.12

RC3 -4.57 -1.82 -2.45

TS3 40.71 47.1 42.75

IC3 8.84 13.91 11.53

I3+HOCl 19.87 23.41 21.88

Table S4: Calculated values (kcal/mol) of ∆ETot, ∆H298 and ∆G298 for the reaction pathways R4, R5 and R6 using M06-2X/6-311+G(d,p), MPWB1K/6-311+G(d,p) methods.

Reaction Channel

M06-2X/

6-311+G(d, p)

MPWB1K/

6-311+G(d,p)

∆ETot ∆H298 ∆G298 ∆ETot ∆H298 ∆G298

R4 4.4 -15.4 -11.6 6.0 -16.7 -9.8

R5 10.5 -27.6 -27.0 12.1 -33.0 -32.5

R6 5.1 -43.0 -45.0 4.4 -40.7 -44.5

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Figure S4: Potential energy surface scan for the peroxy radical intermediate I4 along the dihedral angle (H2-C2-O3-O4) at M06-2X/6-311+G(d,p) level of theory

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Figure S5: Potential energy surface scan for the chloro-hydoxyperoxy-acetic product P, along the dihedral angle (C2-O3-O4-H3) at M06-2X/6-311+G(d,p) level of theory

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Table S5: TST, CVT and TST/SCT rate constants (in cm³molecule^-1s^-1) for the hydrogen abstraction from –C(O)OH site of MCAA with OH radical calculated at M06-2X/6-311+G(d,p) level

T (K) TST (x 10^-14) CVT (x 10^-14) TST /SCT (x 10^-14)

278 7.60 7.59 7.60

288 7.92 7.91 7.92

298 8.25 8.23 8.25

308 8.57 8.55 8.57

318 8.90 8.88 8.90

328 9.23 9.20 9.23

338 9.56 9.53 9.55

348 9.89 9.86 9.89

350 9.95 9.92 9.95

Table S6: TST, CVT and TST/SCT rate constants (in cm³molecule^-1s^-1) for the hydrogen abstraction from –CH2Cl site of MCAA with OH radical calculated at M06-2X/6-311+G(d,p) level

T (K) TST (x 10^-14) CVT (x 10^-14) TST /SCT (x 10^-13)

278 2.32 1.06 1.78

288 2.60 1.23 1.81

298 2.89 1.43 1.85

308 3.21 1.63 1.89

318 3.55 1.86 1.93

328 3.90 2.11 1.97

338 4.27 2.37 2.02

348 4.67 2.65 2.07

350 4.75 2.71 2.08

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Table S7: Comparison of the rate constant values for the reaction of OH radical with acetic acid and Haloacetic acid at 298K

Species KOH cm³molecule^-1s^-1 Techniques/Theoritical

method Reference

CH3COOH

2.0 x10^-13

8.5 x 10^-13

Relative rate technique

Pulsed laser photolysis

40

41

CCl3COOH 2.4 x 10^-13 QASR model 39

CF3COOH 2.1 x 10^-13 5.4 x 10^-14

Relative rate technique QASR model

8 39

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Figure S6: Optimized geometry of the species involved in primary and secondary reactions obtained at M06-2X/6-311+G(d,p) level of theory. The bond lengths given in the structures are in Å.

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Section S8: Cartesian Coordinates (Gaussian, Standard Orientation) of the reactant, reactant complex, transition, intermediate complexes and intermediates involved in the primary reaction at the M06-2X/6-311+G(d,p) level of theory.

MCAA

1 -2.816862000 -0.001036000 -0.000523000 8 -2.065806000 -0.609859000 -0.000487000 6 -0.939544000 0.128346000 0.000141000 6 0.254478000 -0.803158000 0.000619000 1 0.206774000 -1.436123000 0.885670000 17 1.790563000 0.073168000 -0.000281000 1 0.206299000 -1.437780000 -0.883222000 8 -0.924867000 1.319853000 0.000275000

OH

8 0.000000000 0.000000000 0.108003000 1 0.000000000 0.000000000 -0.864024000

RC1

1 -2.108873000 0.884341000 -0.000038000 8 -1.205515000 1.258698000 -0.000028000 6 -0.323476000 0.260692000 -0.000006000 6 1.080394000 0.825319000 0.000031000 1 1.205227000 1.449233000 -0.884158000 17 2.318861000 -0.436222000 -0.000005000 1 1.205203000 1.449151000 0.884283000 8 -0.612422000 -0.905944000 -0.000008000 1 -2.612571000 -1.168872000 -0.000060000 8 -3.388455000 -0.567022000 0.000025000

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TS1

1 -2.277903000 0.457771000 -0.036267000 8 -1.340032000 1.211236000 -0.060608000 6 -0.430790000 0.332984000 0.004839000 6 0.989367000 0.856108000 0.048564000 1 1.123478000 1.538961000 -0.788076000 17 2.227150000 -0.408277000 -0.022952000 1 1.103830000 1.410486000 0.979471000 8 -0.668941000 -0.890388000 0.044110000 1 -2.825197000 -1.121012000 -0.735188000 8 -2.783179000 -0.630854000 0.097726000

IC1

1 -3.663261000 -0.129079000 0.584812000 8 -1.210721000 1.089065000 -0.145609000 6 -0.344984000 0.144109000 0.114519000 6 1.035956000 0.816118000 0.246706000 1 1.109978000 1.687937000 -0.398597000 17 2.323553000 -0.323808000 -0.161653000 1 1.150290000 1.118047000 1.287240000 8 -0.559430000 -1.025834000 0.269861000 1 -2.585348000 -1.031389000 -0.037735000 8 -3.187084000 -0.300998000 -0.231122000

I1

8 -2.121902000 -0.581088000 -0.000015000 6 -0.989804000 0.103004000 0.000003000 6 0.214044000 -0.830714000 0.000017000 1 0.179851000 -1.460821000 0.887945000 17 1.719681000 0.091501000 -0.000007000 1 0.179847000 -1.460861000 -0.887882000

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8 -0.995563000 1.297640000 0.000008000

RC2

1 -1.652192000 2.026899000 0.000206000 8 -1.459147000 1.078695000 0.000251000 6 -0.106221000 0.931106000 0.000099000 6 0.237280000 -0.541900000 0.000176000 1 -0.200274000 -1.011287000 0.880451000 17 1.983286000 -0.811620000 -0.000009000 1 -0.200498000 -1.011444000 -0.879903000 8 0.640598000 1.855719000 -0.000066000 1 -2.699237000 -0.486412000 -0.000107000 8 -2.900202000 -1.441346000 -0.000451000

TS2

1 -2.496449000 -1.211918000 0.067489000 8 -1.922048000 -0.488704000 0.354497000 6 -0.650106000 -0.819245000 0.035346000 6 0.269583000 0.283151000 0.494502000 1 -0.146910000 1.282573000 0.016035000 17 1.925088000 0.073374000 -0.009136000 1 0.203415000 0.428764000 1.571663000 8 -0.347070000 -1.826878000 -0.521691000 1 -1.848110000 1.846797000 -0.174702000 8 -1.000295000 2.268454000 -0.395840000

IC2

1 1.459121000 2.170256000 -0.001485000 8 1.343696000 1.210916000 -0.000060000 6 -0.001366000 0.977597000 0.000033000 6 -0.282766000 -0.443476000 -0.001493000

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1 3.573691000 -1.614625000 0.091814000 17 -1.889835000 -0.956658000 0.001170000 1 0.495819000 -1.193737000 -0.004082000 8 -0.806901000 1.870965000 0.001079000 1 2.678507000 -0.361473000 0.006347000 8 2.666312000 -1.324626000 -0.013983000

I2

1 2.795664000 -0.094813000 -0.000006000 8 2.027554000 -0.680643000 -0.000010000 6 0.926700000 0.103140000 0.000003000 6 -0.276217000 -0.712259000 0.000011000 17 -1.787755000 0.031647000 -0.000005000 1 -0.243592000 -1.790754000 0.000037000 8 0.964554000 1.305927000 0.000006000

RC3

1 3.050272000 1.067878000 0.000010000 8 2.105350000 1.272646000 0.000041000 6 1.434006000 0.105794000 -0.000014000 6 -0.050206000 0.397037000 0.000023000 1 -0.310115000 0.980356000 0.881529000 17 -1.015010000 -1.091459000 0.000037000 1 -0.310147000 0.980360000 -0.881472000 8 1.960422000 -0.964003000 -0.000081000 1 -3.507209000 0.511908000 -0.000083000 8 -2.812077000 1.191021000 -0.000044000

TS3

1 2.691110000 -1.136738000 0.327992000 8 1.866145000 -0.836335000 0.731974000

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6 1.451293000 0.247204000 0.047079000 6 0.167013000 0.755459000 0.550004000 1 -0.110453000 0.535654000 1.571591000 17 -1.259037000 -0.664300000 -0.429562000 1 -0.183699000 1.676581000 0.108266000 8 2.050007000 0.700373000 -0.892553000 1 -3.228305000 0.307157000 0.102754000 8 -2.350509000 0.622769000 0.361761000

IC3

1 -2.878651000 -0.779893000 -0.973154000 8 -2.677344000 0.068276000 -0.555503000 8 -0.889042000 -1.113925000 0.080108000 6 -1.504588000 -0.061646000 0.082281000 6 -1.073037000 1.145057000 0.748862000 1 -0.159450000 1.117510000 1.324242000 1 -1.663171000 2.046002000 0.674068000 17 2.013843000 0.319292000 -0.555125000 8 1.703093000 -0.614987000 0.825653000 1 0.838044000 -1.026960000 0.623040000

I3

1 1.753723000 -0.608379000 0.000012000 8 0.852097000 -0.954324000 -0.000011000 6 0.017775000 0.110995000 -0.000003000 6 -1.377517000 -0.271948000 0.000003000 1 -2.116757000 0.514145000 -0.000094000 1 -1.665090000 -1.312744000 0.000091000 8 0.421224000 1.250911000 0.000010000

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H₂O

8 0.000000000 0.000000000 0.116592000 1 0.000000000 0.761679000 -0.466367000 1 0.000000000 -0.761679000 -0.466367000

HOCl

17 0.036002000 -0.596669000 0.000000000 8 0.036002000 1.100888000 0.000000000 1 -0.900048000 1.336270000 0.00000000

I2 + O2

1 -2.763726000 -1.115235000 0.001195000 8 -2.192023000 -0.624238000 -0.603206000 6 -1.255446000 -0.006057000 0.147788000 6 -0.339758000 0.743327000 -0.698524000 17 0.920430000 1.612400000 0.006366000 1 -0.431881000 0.766202000 -1.773384000 8 -1.199866000 -0.087150000 1.347018000 8 1.060797000 -1.723004000 -0.427752000 8 1.971033000 -1.501279000 0.304988000

TS4

1 2.936821000 0.686448000 -0.032042000 8 2.151257000 0.596150000 -0.587869000 6 1.269354000 -0.174773000 0.074330000 6 0.016328000 -0.267354000 -0.694618000 17 -1.193393000 -1.296544000 -0.135794000 1 0.011111000 -0.028797000 -1.748479000 8 1.472445000 -0.667778000 1.147655000 8 -0.691044000 1.589553000 -0.093627000 8 -1.729451000 1.486619000 0.510182000

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I4

1 -2.829875000 -0.419302000 0.033013000 8 -2.064986000 0.045924000 0.399345000 6 -0.962403000 -0.617110000 0.039989000 6 0.266648000 0.101804000 0.618294000 17 1.763011000 -0.578646000 -0.004757000 1 0.269392000 0.022152000 1.704534000 8 -0.936176000 -1.631581000 -0.578950000 8 0.197326000 1.502417000 0.360654000 8 -0.100686000 1.748986000 -0.881845000 I4 + NO

1 -2.373949000 -2.127445000 0.350766000 8 -1.852694000 -1.622730000 -0.288735000 6 -1.550957000 -0.444713000 0.264995000 6 -0.709075000 0.374902000 -0.729922000 17 -0.178731000 1.897495000 0.015706000 1 -1.309269000 0.619721000 -1.606281000 8 -1.907820000 -0.078836000 1.339329000 8 0.350803000 -0.370925000 -1.238692000 8 1.046516000 -0.935347000 -0.161191000 7 2.288607000 -0.176887000 -0.021850000 8 2.895894000 -0.628739000 0.840667000

TS5

1 2.462593000 -2.108525000 -0.244490000 8 1.837508000 -1.657610000 0.339347000 6 1.622541000 -0.434680000 -0.156170000 6 0.611326000 0.295993000 0.743717000 17 0.222930000 1.896416000 0.068364000 1 1.041090000 0.449958000 1.733941000

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8 2.160201000 0.020968000 -1.114743000 8 -0.519246000 -0.478045000 0.967487000 8 -0.969642000 -0.984292000 -0.268388000 7 -2.224990000 -0.083781000 -0.616228000 8 -3.149043000 -0.546261000 -0.156621000

I5 + NO2

1 2.343815000 -2.346843000 0.233836000 8 1.522021000 -1.872903000 0.423279000 6 1.670905000 -0.604482000 0.030820000 6 0.365502000 0.155713000 0.311547000 17 0.516027000 1.872902000 -0.070747000 1 0.108953000 0.065128000 1.366203000 8 2.659205000 -0.135924000 -0.434110000 8 -0.600218000 -0.469689000 -0.493184000 8 -2.717574000 -0.772088000 -0.805296000 7 -1.938949000 -0.330541000 -0.032929000 8 -2.097310000 0.181701000 1.031679000 I4 + HO₂

1 -2.644846000 -1.945096000 0.492340000 8 -2.155047000 -1.471749000 -0.194766000 6 -1.657440000 -0.355850000 0.339567000 6 -0.837105000 0.377136000 -0.737144000 17 -0.095466000 1.851447000 -0.028330000 1 -1.471003000 0.696420000 -1.562800000 8 -1.840470000 0.023559000 1.451903000 8 0.125929000 -0.453931000 -1.295134000 8 0.824494000 -1.066929000 -0.301424000 8 2.324560000 -0.124920000 -0.011238000 8 3.084111000 -0.767449000 0.780460000 1 1.797432000 0.537704000 0.499117000

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TS6

1 -2.771205000 -1.877816000 0.493692000 8 -2.334052000 -1.364533000 -0.199976000 6 -1.674079000 -0.358949000 0.379031000 6 -0.909980000 0.412343000 -0.712099000 17 -0.097623000 1.838061000 0.015192000 1 -1.583990000 0.771691000 -1.487434000 8 -1.686704000 -0.103304000 1.541233000 8 0.008231000 -0.409462000 -1.346202000 8 0.776060000 -1.037157000 -0.407342000 8 2.506746000 -0.073412000 0.013500000 8 3.220534000 -0.827360000 0.685782000 1 1.592617000 0.060541000 0.437930000

P

1 -3.327038000 -1.258899000 0.097902000 8 -2.483644000 -1.170598000 -0.366670000 6 -1.924197000 -0.019461000 0.016350000 6 -0.571167000 0.136308000 -0.698455000 17 0.261425000 1.612174000 -0.118265000 1 -0.726585000 0.250584000 -1.771448000 8 -2.417616000 0.770679000 0.757110000 8 0.215668000 -0.989106000 -0.562718000 8 0.230849000 -1.352277000 0.808203000 8 2.820567000 0.014401000 0.559393000 8 3.323470000 -0.540896000 -0.361280000 1 1.067244000 -0.957339000 1.104375000