{"id":29711,"date":"2025-12-16T16:00:46","date_gmt":"2025-12-16T16:00:46","guid":{"rendered":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29711"},"modified":"2025-12-16T16:17:53","modified_gmt":"2025-12-16T16:17:53","slug":"mechanism-of-reaction-between-titanocene-pentasulfide-and-sulfenyl-chloride-the-effect-of-continuum-solvation-on-the-energy-surface","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29711","title":{"rendered":"Mechanism of reaction between titanocene pentasulfide and sulfenyl chloride: The effect of continuum solvation on the energy surface."},"content":{"rendered":"
\n

An investigation of the kinetics of the reaction between titanocene pentasulfide and sulfenyl chloride[1]<\/a><\/span> leading to the formation of the S7<\/sub> allotrope of sulfur was accompanied by supporting DFT calculations which led to the conclusion\u00a0that of five possible\u00a0mechanisms for the reaction, the most probable corresponded to a variant of the concerted \u03c3-bond metathesis (Scheme 1, Mechanism IV, R = Cl). Here we take a closer look at the DFT predictions from the point of view of the impact of continuum solvation on the calculated mechanism.<\/p>\n

\"\"<\/p>\n

Scheme 1.<\/strong> \u00a0Possible reaction mechanisms.<\/p>\n

The original study used the new r2<\/sup>scan-3c\/Def2-mTZVPP<\/strong> composite DFT functional[2]<\/a><\/span> as implemented in the ORCA 6 program code,[3]<\/a><\/span> for which the (gas phase) mechanistic reported pathway was obtained as shown in scheme 2 below. Here, we re-label the succeeding steps as TS3<\/strong>\u00a0and TS4<\/strong> (see Scheme 3 below, rather than TS2<\/strong> from scheme 2) to form the final product P<\/strong>, for reasons that will become apparent below.
\n\"\"<\/p>\n

Scheme 2. \u00a0<\/strong>Reaction \u00a0scheme and energy profile.[1]<\/a><\/span><\/p>\n

Methodology<\/h3>\n

In this study, we\u00a0used an older functional, MN15L<\/strong>[4]<\/a><\/span> for R=Cl (scheme 1), which we have found very effective for the transition elements[5]<\/a><\/span> and which –\u00a0like r2<\/sup>scan-3c<\/strong> – was\u00a0designed to be accurate for multi-reference and single-reference systems and for noncovalent interactions<\/a><\/em>, This functional, unlike r2<\/sup>scan-3c<\/strong>, is implemented in the Gaussian 16 program code and hence has the advantage of allowing computed intrinsic reaction coordinate (IRC) data to be usefully visualised using e.g.<\/em> Gaussview.\u2021<\/sup> Transition state geometries were initially obtained from the supporting information given in the original article [1]<\/a><\/span> and re-optimised in the Gaussian program using MN15L\/Def2-TZVPP. The thermochemical energies shown in Table A1 were all obtained using GoodVibes[6]<\/a><\/span> (see manual<\/a>) with an entropic quasi-harmonic treatment frequency cut-off value of 2.0 wavenumbers[7]<\/a><\/span> and an enthalpic quasi-harmonic treatment frequency cut-off value of 50.0 wavenumbers.[8]<\/a><\/span> In the table, harmonic values are indicated as e.g. hG\u00a0and quasi-harmonic values as qh-G; the difference between these two is relative small. If desired, other harmonic cut-off values can be obtained, as well as at other molar concentrations, using log files obtained from the repository DOIs indicated below, via<\/em> the command line:<\/p>\n

python3 -m goodvibes -q --fs 2 --fh 50 -c 0.0409 logfilename<\/tt>.<\/p>\n

Results<\/h3>\n

Part 1: Gas phase model<\/h4>\n

The intrinsic reaction coordinate (IRC) deriving from transition state TS1<\/strong> computed using Gaussian 16, and without inclusion of a solvent continuum model (a gas phase model) is shown below (Table 1, Figure 1).[9]<\/a><\/span> It leads directly to the “half-way” product Int2<\/strong>, with no intervening intermediate such as that shown in Scheme 2 (there labelled Int1<\/strong>[1]<\/a><\/span>). So here, the TS1<\/strong> IRC conflates the originally reported TS1<\/strong> and TSint<\/strong>[1]<\/a><\/span> as shown in scheme 2, with the conflation point occuring at an IRC value of ~9. This\u00a0point can also be seen below as a prominent “hidden intermediate<\/em>” in the\u00a0gradient norm plot at the same IRC value. A gradient norm at this point of not quite zero is what makes it a “hidden” rather than a “real” intermediate. The conflation point also ~corresponds to a minimum in the dipole moment plot.\u00a0Here,[9]<\/a><\/span>\u00a0the stepsize between points in the IRC calculation was selected as 20 (in units of 0.01 Bohr) and the Hessian was recalculated every 5 steps. The equivalent parameters for the IRCs as noted – but not visualised –\u00a0in the original article[1]<\/a><\/span> were not stated; it is entirely possible that differences in either these parameters, or the algorithms used to compute the IRC or indeed the use of a different functional could account for this slight difference in behaviour. Slight, because TSint<\/strong> is shown as a very shallow intermediate (Scheme 2[1]<\/a><\/span>).<\/p>\n

\"\"
\nFigure 1.<\/strong> Computed geometry of TS1<\/strong> in the gas phase at the MN15L\/Def2-TZVPP level.<\/p>\n\n\n\n\n\n\n
Table 1. IRC for TS1 in a gas phase MN15L\/Def2-TZVPP model.<\/th>\n<\/tr>\n
Total Energy<\/td>\n\"\"<\/td>\n<\/tr>\n
\u00a0Gradient norm<\/td>\n\"\"<\/td>\n<\/tr>\n
Dipole moment<\/td>\n\"\"<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

<\/p>\n

Part 2: Continuum solvent model (scheme 3).<\/h4>\n

FAIR data for all the calculations conducted using a dichloromethane continuum solvent are summarised here, [10]<\/a><\/span> with individual calculations indicated as a reference to a FAIR repository dataset \u00a0(Table A1). The computed geometry of TS1<\/strong> changes from the initial values of a) the new S7<\/sub>-S8<\/sub> bond 2.195 \u2192 2.356\u00c5, b) S8<\/sub>-Cl 2.918 \u2192 2.616\u00c5 and\u00a0c) S7<\/sub>-Ti 2.572 \u2192 2.562\u00c5 (Table 2, atom numbering shown in \u00a0Figure 1).
\n\"\"<\/a><\/p>\n

Scheme 3. \u00a0<\/strong>Revised reaction scheme showing the formation of the ion-pair Int0<\/strong> rather than Int1<\/strong>\u00a0computed using geometries optimised with continuum solvation effects included.<\/p>\n\n\n\n\n\n\n\n
Table 2. Calculated geometries for TS1 – Ts4 with solvation<\/th>\n<\/tr>\n
#<\/th>\nGeometry<\/th>\n#<\/th>\nGeometry<\/th>\n<\/tr>\n
TS1<\/td>\n\"\"<\/td>\nInt0<\/td>\n\"\"<\/td>\n<\/tr>\n
TS2<\/td>\n\"\"<\/td>\nInt2<\/td>\n\"\"<\/td>\n<\/tr>\n
TS3<\/td>\n\"\"<\/td>\nTS4<\/td>\n\"\"<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

When same potential energy surface is computed with a continuum solvent model (Table 3), the “hidden intermediate” present for the gas phase model in the original IRC profile of TS1<\/strong> (Table 1) now becomes a real ion-pair intermediate (labelled here Int0<\/strong> in \u00a0scheme 3<\/strong> to distinguish it from Int1<\/strong> in scheme 2<\/strong>) with a discrete chloride anion. Thus Int0<\/strong> occurs at an IRC value of ~3.5\u00a0in the plots below, although it has a very small exit barrier via<\/em> a transition state,\u00a0here labelled TS2<\/strong> (different from the TS2 labelled in scheme 2 above). The plots below \u00a0(Table 3) are the result of concatenating two separate IRC plots for TS1<\/strong> and TS2<\/strong>.<\/p>\n\n\n\n\n\n\n
Table 3. IRCs for TS1 + TS2 in a continuum solvent model<\/th>\n<\/tr>\n
\"\"<\/td>\n<\/tr>\n
\"\"<\/td>\n<\/tr>\n
\"\"<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The gas phase (left) and continuum solvent (right) IRCs are summarised below (Figure 2<\/strong>) to enable a visual comparison of the two potential energy surfaces.<\/p>\n

\"\"<\/a><\/p>\n

Figure 2<\/strong>. A comparison of the computed\u00a0IRC energy profiles in the gas phase (left) and continuum dichloromethane solvent (right).<\/p>\n

This indicates a change from Mechanism IV under gas phase conditions (scheme 2) to one closer to mechanism II with continuum solvent; an SN<\/sub>2 like displacement of chloride ion at sulfur, followed in a second step by Cl…Ti bond formation and Ti…S cleavage, Scheme 3. This can also be summarised by the following plots of bond lengths in Figure 3.<\/p>\n

\"\"<\/p>\n

Figure 3.<\/strong> Selected bond length variation for the concatenated IRC profile for\u00a0TS1 + TS2 in a continuum solvent. See Figure 1 for atom numberings.<\/p>\n

The overall results can be summarised in Table 4 indicting that both the original r2<\/sup>scan-3c\/Def2-mTZVPP <\/strong>and the MN15L<\/strong> functional used here are both in reasonable agreement with the experimental results obtained from kinetic studies. Also noteworthy is that for substituents such as e.g. 2b<\/strong>, the enthalpy of activation\u00a0may actually be negative, with the resulting positive value for the free energy of activation being a consequence of a very negative entropy of activation.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Table 4. Solvent DCM model: Mechanism II through to Ion-Pair intermediate Int0 rather than the original Int1.<\/th>\n<\/tr>\n
Source<\/th>\n\u0394H<\/td>\n\u0394S<\/td>\n\u0394G<\/td>\n<\/tr>\n
1a: Article<\/td>\n6.0<\/td>\n-45.7<\/td>\n19.6<\/td>\n<\/tr>\n
1a: This work<\/td>\n3.4<\/td>\n-31.5<\/td>\n12.8<\/td>\n<\/tr>\n
1a: Expt\/1M<\/td>\n0.0<\/td>\n-49.7<\/td>\n14.8<\/td>\n<\/tr>\n
2a: Article<\/td>\n1.7<\/td>\n-45.7<\/td>\n15.3<\/td>\n<\/tr>\n
2a: This work<\/td>\n0.8<\/td>\n-39.5<\/td>\n12.6<\/td>\n<\/tr>\n
2a: Expt\/1M<\/td>\n-2.3<\/td>\n-48.2<\/td>\n12.6<\/td>\n<\/tr>\n
2b: Article<\/td>\n<\/td>\n<\/td>\n~10.8<\/td>\n<\/tr>\n
2b: This work<\/td>\n-1.4<\/td>\n-34.1<\/td>\n8.80<\/td>\n<\/tr>\n
6m: Article<\/td>\n<\/td>\n<\/td>\n~25.0<\/td>\n<\/tr>\n
6m: This work<\/td>\n8.95<\/td>\n-39.2<\/td>\n20.6<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Conclusions<\/h2>\n

The overall conclusion is simple; when the possibility of ion-pair formation on a reaction potential energy surface is present, it matters how the geometries of all the species involved are obtained. A gas phase geometry optimised model is likely to disfavour the formation of such an ion-pair, whereas a continuum solvent geometry optimised model is more likely to promote such species. This effect can be seen especially in Figure 2, where the two potentials are shown side by side. Such promotion of ion-pairs is likely to reduce any concerted behaviour of the reaction into a two-stage stepwise process. Thus the concerted nature of mechanism IV (Scheme 1) morphs into more stepwise behaviour (Mechanism II, Scheme 1 modified as in Scheme 3). Overall however, while the resulting calculated energetic barriers, although reduced by inclusion of solvation, are unlikely provide definitive evidence of which mechanism actually prevails, the greater change in dipole moment in the stepwise behaviour is more consistent with the experimentally observed effects of solvent identity on the rate.<\/p>\n

\n

Appendix<\/h2>\n

All energies for the computed species, obtained with optimisation with a dichloromethane continuum solvent model. Values for the default concentration of 0.0409M are shown for completeness and to enable facile reconciliation with those included in the published FAIR datasets.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Table A1. Calculations at the MN15L\/Def2-TZVPP; Def2-QZVPP on Ti\/CPCM=Dichloromethane level with geometry optimisation.<\/th>\n<\/tr>\n
1a (scheme 2)<\/th>\n<\/tr>\n
Species<\/th>\nh-H<\/th>\nT.h-S<\/th>\nh-G<\/th>\nqh-H<\/th>\nT.qh-S<\/th>\nqh-G<\/th>\n<\/tr>\n
Z=S<\/td>\n-3227.1212a<\/sup>
\n-3227.1212b<\/sup><\/td>\n		0.05845
\n0.05543<\/td>\n		-3227.179639
\n[11]<\/a><\/span>
\n-3227.176621<\/td>\n		-3227.12140
\n-3227.12140<\/td>\n		0.05845
\n0.05543<\/td>\n		-3227.17985
\n-3227.17683
\n<\/td>\n<\/tr>\n
S2Cl2<\/td>\n-1716.63131a<\/sup>
\n-1716.63135b<\/sup><\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.667668
\n[12]<\/a><\/span>
\n-1716.664658<\/td>\n		-1716.63135
\n-1716.63135<\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.66771
\n-1716.66470<\/td>\n<\/tr>\n
Sum<\/td>\n-4943.75254a<\/sup>
\n-4943.75254b<\/sup><\/td>\n		0.09481
\n0.08878<\/td>\n		-4943.847307
\n-4943.841279
\n<\/td>\n		-4943.75275
\n-4943.75275<\/td>\n		0.09481
\n0.08878<\/td>\n		-4943.84756
\n-4943.84152<\/td>\n<\/tr>\n
TS1<\/td>\n-4943.74534a<\/sup>
\n-4943.74534b<\/sup><\/td>\n		0.07984
\n0.07682<\/td>\n		-4943.825172<\/a>
\n[13]<\/a><\/span>
\n-4943.822153<\/td>\n		-4943.74734
\n-4943.74734<\/td>\n		0.07984
\n0.07682<\/td>\n		-4943.82717
\n-4943.82415<\/td>\n<\/tr>\n
\u0394TS1<\/td>\n4.52<\/td>\n-31.53<\/td>\n13.88 <\/td>\n3.39<\/strong><\/td>\n-31.52<\/strong><\/td>\n12.79<\/strong><\/td>\n<\/tr>\n
\u0394TS1b<\/sup><\/td>\n4.52<\/td>\n-25.17<\/td>\n12.00<\/td>\n3.39<\/td>\n-25.17<\/td>\n10.90<\/strong><\/td>\n<\/tr>\n
Int0c<\/sup><\/td>\n-4943.75128<\/td>\n0.08039<\/td>\n-4943.831670
\n[14]<\/a><\/span> <\/td>\n		-4943.75298<\/td>\n0.08039<\/td>\n-4943.83337<\/td>\n<\/tr>\n
\u0394Int0<\/td>\n0.76<\/td>\n-30.36<\/td>\n9.81\u00a0<\/td>\n-0.15<\/td>\n-30.36<\/td>\n8.91<\/td>\n<\/tr>\n
TS2<\/td>\n-4943.74951<\/td>\n0.07801<\/td>\n-4943.827519<\/a>
\n[15]<\/a><\/span><\/td>\n		-4943.75100<\/td>\n0.07801<\/td>\n-4943.82901<\/td>\n<\/tr>\n
\u0394TS2<\/td>\n1.88<\/td>\n-35.33<\/td>\n12.42<\/td>\n1.10<\/td>\n-35.36<\/td>\n11.64<\/td>\n<\/tr>\n
Int2<\/td>\n-4943.79255<\/td>\n0.08031<\/td>\n-4943.872859
\n[16]<\/a><\/span><\/td>\n		-4943.79432<\/td>\n0.08031<\/td>\n-4943.87463<\/td>\n<\/tr>\n
\u0394Int2<\/td>\n-25.13<\/td>\n-30.53<\/td>\n-16.03<\/td>\n-26.09<\/td>\n-30.53<\/td>\n-16.99 (-11.0 lit)<\/td>\n<\/tr>\n
TS3<\/td>\n-4943.77886<\/td>\n0.08003<\/td>\n-4943.858887
\n[17]<\/a><\/span><\/td>\n		-4943.78065<\/td>\n0.08003<\/td>\n-4943.86068<\/td>\n<\/tr>\n
\u0394TS3<\/td>\n-16.54<\/td>\n-30.12<\/td>\n-7.27<\/td>\n-4943.78065<\/td>\n<\/td>\n-8.23<\/td>\n<\/tr>\n
Int3<\/td>\n-4943.78456<\/td>\n\u00a0<\/span>0.079887<\/td>\n-4943.864446
\n[18]<\/a><\/span><\/td>\n		-4943.78619<\/td>\n0.079887<\/td>\n-4943.86607<\/td>\n<\/tr>\n
\u0394Int3<\/td>\n-20.12<\/td>\n\u00a0-31.42<\/td>\n-10.76<\/td>\n-20.98<\/td>\n-31.42<\/td>\n-11.62<\/td>\n<\/tr>\n
TS4<\/td>\n-4943.78439<\/td>\n0.07807<\/td>\n-4943.862461<\/a>
\n[19]<\/a><\/span><\/td>\n		-4943.78599<\/td>\n0.07807<\/td>\n-4943.86406<\/td>\n<\/tr>\n
\u0394TS4<\/td>\n-20.01<\/td>\n-35.23<\/td>\n-9.51<\/td>\n-20.86<\/td>\n-35.23<\/td>\n-10.36<\/td>\n<\/tr>\n
S7 as product<\/td>\n-2787.10568<\/td>\n0.04667<\/td>\n-2787.152347
\n[20]<\/a><\/span><\/td>\n		-2787.10608<\/td>\n0.04667<\/td>\n-2787.15275<\/td>\n<\/tr>\n
Cp2TiCl2<\/td>\n-2156.70450<\/td>\n0.04990<\/td>\n-2156.754401
\n[21]<\/a><\/span><\/td>\n		-2156.70456<\/td>\n0.04990<\/td>\n-2156.75447<\/td>\n<\/tr>\n
Product P<\/td>\n-4943.81017<\/td>\n0.09657<\/td>\n-4,943.906749<\/td>\n-4943.81064<\/td>\n0.09657<\/td>\n-4,943.90722<\/td>\n<\/tr>\n
\u0394Product P<\/td>\n-36.19<\/td>\n3.70<\/td>\n-37.30<\/td>\n-36.33<\/td>\n3.70<\/td>\n-37.43
\n(-36.9 lit)<\/td>\n<\/tr>\n
2a:<\/th>\n<\/tr>\n
Z=CMe2<\/td>\n-2946.72598a<\/sup>
\n-2946.72598b<\/sup><\/td>\n		0.06683
\n0.063808<\/td>\n		-2946.7928059
\n[22]<\/a><\/span>–2946.789786<\/td>\n		-2946.72674
\n-2946.72674<\/td>\n		0.06683
\n0.063806<\/td>\n		-2946.79356
\n-2946.790542<\/td>\n<\/tr>\n
S2Cl2<\/td>\n-1716.63131a<\/sup>
\n-1716.63135b<\/sup><\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.667668
\n[12]<\/a><\/span>
\n-1716.664658<\/td>\n		-1716.63135
\n-1716.63135<\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.66771
\n-1716.66470<\/td>\n<\/tr>\n
Sum<\/td>\n-4663.35729
\n-4663.35729<\/td>\n		0.10319
\n0.097158<\/td>\n		-4663.4604739
\n-4,663.454444
\n<\/td>\n		-4663.35808
\n-4663.35808<\/td>\n		0.10319
\n0.097156<\/td>\n		-4663.46127
\n-4663.455242<\/td>\n<\/tr>\n
TS1<\/td>\n-4663.35477a<\/sup>
\n-4663.35477b<\/span><\/td>\n		0.08445
\n0.081429<\/td>\n		-4663.439222
\n[23]<\/a><\/span>-4663.436203<\/td>\n		-4663.35677
\n-4663.35677<\/td>\n		0.08445
\n0.081429<\/td>\n		-4663.44122
\n-4663.438201<\/td>\n<\/tr>\n
\u0394TS1a<\/sup><\/td>\n1.58<\/td>\n-39.45<\/td>\n13.34<\/td>\n0.82<\/td>\n-39.46<\/td>\n12.59<\/strong><\/td>\n<\/tr>\n
\u0394TS1b<\/sup><\/td>\n1.58<\/td>\n-33.10<\/td>\n11.45<\/td>\n<\/td>\n-33.10<\/td>\n10.69<\/strong><\/td>\n<\/tr>\n
TS2<\/td>\n-4663.36425<\/td>\n0.08207<\/td>\n-4663.446325
\n[24]<\/a><\/span><\/td>\n		-4663.36574<\/td>\n0.08207<\/td>\n-4663.44782<\/td>\n<\/tr>\n
\u0394TS2<\/td>\n-4.37<\/td>\n-44.44<\/td>\n8.88<\/td>\n-4.80<\/td>\n-44.44<\/td>\n8.44<\/td>\n<\/tr>\n
2b:<\/th>\n<\/tr>\n
Z=C(NMe2)2<\/td>\n-3135.79512
\n-3135.79512<\/td>\n		0.07575<\/p>\n

0.072730<\/td>\n

-3135.870870
\n[25]<\/a><\/span>-3135.867852<\/td>\n		-3135.79611
\n-3135.79611<\/td>\n		\u00a0<\/span>0.07575
\n0.072730<\/td>\n		-3135.87186
\n-3135.86884<\/td>\n<\/tr>\n
S2Cl2<\/td>\n-1716.63131a<\/sup>
\n-1716.63135b<\/sup><\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.667668
\n[12]<\/a><\/span>
\n-1716.664658<\/td>\n		-1716.63135
\n-1716.63135<\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.66771
\n-1716.66470<\/td>\n<\/tr>\n
Sum<\/td>\n-4852.4264
\n-4852.4264<\/td>\n		0.11212
\n0.10608<\/td>\n		-4852.538538
\n-4852.53251<\/td>\n		-4852.42745
\n-4852.42745<\/td>\n		0.11212
\n0.10608<\/td>\n		-4852.5396
\n-4852.53354<\/td>\n<\/tr>\n
TS1<\/td>\n-4852.42719
\n-4852.42719<\/td>\n		0.09602
\n0.09300<\/td>\n		-4852.523215
\n[26]<\/a><\/span>
\n-4852.520196
\n<\/td>\n		-4852.42964
\n-4852.42964<\/td>\n		0.09591
\n0.09289<\/td>\n		-4852.52555
\n-4852.522536<\/td>\n<\/tr>\n
\u0394TS1a<\/sup><\/td>\n-0.49<\/td>\n-33.86<\/td>\n9.62 <\/td>\n-1.37<\/td>\n-34.11<\/td>\n8.80<\/strong><\/td>\n<\/tr>\n
\u0394TS1b<\/sup><\/td>\n-0.49<\/td>\n-27.53<\/td>\n7.27<\/td>\n-1.37<\/td>\n-27.76<\/td>\n6.91<\/strong><\/td>\n<\/tr>\n
TS2<\/td>\n-4852.43669<\/td>\n0.09143<\/td>\n-4852.528126
\n[27]<\/a><\/span><\/td>\n		-4852.43823<\/td>\n0.09143<\/td>\n-4852.52966<\/td>\n<\/tr>\n
\u0394TS2<\/td>\n-6.44<\/td>\n-43.54<\/td>\n6.53<\/td>\n-6.76<\/td>\n-43.54<\/td>\n6.22<\/td>\n<\/tr>\n
6m:<\/th>\n<\/tr>\n
Z=C(CN)2<\/td>\n-3052.59951
\n-3052.59951<\/td>\n		0.06956
\n0.06654<\/td>\n		-3052.669074
\n[28]<\/a><\/span>
\n-3052.666055
\n<\/td>\n		-3052.60050
\n-3052.60050<\/td>\n		0.06956
\n0.06654<\/td>\n		-3052.67007
\n-3052.66705<\/td>\n<\/tr>\n
S2Cl2<\/td>\n-1716.63131a<\/sup>
\n-1716.63135b<\/sup><\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.667668
\n[12]<\/a><\/span>
\n-1716.664658<\/td>\n		-1716.63135
\n-1716.63135<\/td>\n		0.03637
\n0.03335<\/td>\n		-1716.66771
\n-1716.66470<\/td>\n<\/tr>\n
Sum<\/td>\n-4769.23082
\n-4769.23082<\/td>\n		0.10593
\n0.09989<\/td>\n		-4769.336742
\n-4769.330713 <\/td>\n		-4769.23185
\n-4769.23185<\/td>\n		0.10593
\n0.09989<\/td>\n		-4769.3378
\n-4769.33175<\/td>\n<\/tr>\n
TS1<\/td>\n-4769.21540a<\/sup>
\n-4769.21540b<\/sup><\/td>\n		0.08731
\n0.08423<\/td>\n		-4769.30271
\n[29]<\/a><\/span>
\n-4769.29970
\n<\/td>\n		-4769.21759
\n-4769.21759<\/td>\n		0.08731
\n0.08423<\/td>\n		-4769.30490
\n-4769.30188<\/td>\n<\/tr>\n
\u0394TS1a<\/sup><\/td>\n9.68<\/td>\n-39.18<\/td>\n21.36 <\/td>\n8.95<\/td>\n-39.18<\/td>\n20.63<\/strong><\/td>\n<\/tr>\n
\u0394TSb<\/sup><\/td>\n9.68<\/td>\n-32.83<\/td>\n19.46<\/td>\n8.95<\/td>\n-32.83<\/td>\n18.74<\/strong><\/td>\n<\/tr>\n
TS2<\/td>\n-4769.22451<\/td>\n0.08582<\/td>\n-4769.310328
\n[30]<\/a><\/span><\/td>\n		-4769.22626<\/td>\n0.08582<\/td>\n-4769.31208<\/td>\n<\/tr>\n
\u0394TS2<\/td>\n3.96<\/td>\n-42.32<\/td>\n16.58<\/td>\n3.51<\/td>\n-42.32<\/td>\n16.13<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

a<\/sup>0.0409M b<\/sup>1.0M c<\/sup>Int0<\/strong> is ion pair comprising S+<\/sup> and Cl–<\/sup> See Table 3 and scheme 3.<\/p>\n

\n

Footnotes<\/h2>\n

\u2021<\/sup>Currently at least, Gaussian is better supported by associated visualisation programs then ORCA.<\/small><\/p>\n

\n

This post has DOI: 10.59350\/1a48f-rj714<\/a><\/p>\n

References<\/h2>\n
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    An investigation of the kinetics of the reaction between titanocene pentasulfide and sulfenyl chloride leading to the formation of the S7 allotrope of sulfur was accompanied by supporting DFT calculations which led to the conclusion\u00a0that of five possible\u00a0mechanisms for the reaction, the most probable corresponded to a variant of the concerted \u03c3-bond metathesis (Scheme 1, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"federated","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1086],"tags":[],"ppma_author":[2661,2667,2666,2664,2665],"class_list":["post-29711","post","type-post","status-publish","format-standard","hentry","category-reaction-mechanism-2"],"yoast_head":"\nMechanism of reaction between titanocene pentasulfide and sulfenyl chloride: The effect of continuum solvation on the energy surface. - 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The role of water in the mechanism of its aqueous racemisation.","author":"Henry Rzepa","date":"November 10, 2012","format":false,"excerpt":"Thalidomide is a chiral molecule, which was sold in the 1960s as a sedative in its (S,R)-racemic form. The tragedy was that the (S)-isomer was tetragenic, and only the (R) enantiomer acts as a sedative. What was not appreciated at the time is that interconversion of the (S)- and (R)\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/11\/thal1.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":27784,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=27784","url_meta":{"origin":29711,"position":1},"title":"Mechanism of the Masamune-Bergman reaction. Part 4. Why was the DFT energy barrier too high for the Calicheamicin reaction?","author":"Henry Rzepa","date":"October 29, 2024","format":false,"excerpt":"Michael in a comment here on the mechanism of the Masamune-Bergman reaction notes that when it occurs as part of the Calicheamicin (an antibody-drug conjugate or ADC) version of this mechanism, a pre-step is first necessary. As discussed in this review article, the trisulfide linkage is reduced and the resulting\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":10015,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10015","url_meta":{"origin":29711,"position":2},"title":"A sideways look at the mechanism of ester hydrolysis.","author":"Henry Rzepa","date":"March 29, 2013","format":false,"excerpt":"The mechanism of ester hydrolysis is a staple of examination questions in organic chemistry. To get a good grade, one might have to reproduce something like the below. Here, I subject that answer to a reality check. In this scheme, HA is a general acid, R=Me, and the net result\u2026","rel":"","context":"In \"ALSO\"","block_context":{"text":"ALSO","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=also"},"img":{"alt_text":"acyl-ester","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/acyl-ester.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":6816,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6816","url_meta":{"origin":29711,"position":3},"title":"The mechanism (in 4D) of the reaction between thionyl chloride and a carboxylic acid.","author":"Henry Rzepa","date":"May 25, 2012","format":false,"excerpt":"If you have not previously visited, take a look at Nick Greeves' ChemTube3D\u00a0, an\u00a0ever-expanding gallery of reactions and their mechanisms. The 3D is because all molecules are offered with X, Y and z coordinates. You also get arrow pushing\u2021\u00a0in 3D. Here, I argue that we should adopt Einstein, and go\u2026","rel":"","context":"In \"acetic acid\"","block_context":{"text":"acetic acid","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=acetic-acid"},"img":{"alt_text":"","src":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/05\/thionyl.svg","width":350,"height":200},"classes":[]},{"id":21363,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21363","url_meta":{"origin":29711,"position":4},"title":"Catalytic Mitsunobu reaction.","author":"Henry Rzepa","date":"October 9, 2019","format":false,"excerpt":"If, as a synthetic chemist, you want to invert the configuration of an alcohol in which the OH group is at a chiral centre, then the Mitsunobu reaction has been a stalwart for many years. Now a catalytic version has been published, along with a proposed mechanism. Here I apply\u2026","rel":"","context":"In "reaction mechanism"","block_context":{"text":"reaction mechanism","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1086"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":14601,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14601","url_meta":{"origin":29711,"position":5},"title":"Yes, no, yes. Computational mechanistic exploration of (nickel-catalysed) cyclopropanation using tetramethylammonium triflate.","author":"Henry Rzepa","date":"October 1, 2015","format":false,"excerpt":"A fascinating re-examination has appeared of a reaction first published in 1960 by Wittig and then repudiated by him in 1964 since it could not be replicated by a later student. According to the new work, the secret to a successful replication\u00a0seems to be\u00a0the presence of traces of a nickel\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""},{"term_id":2667,"user_id":0,"is_guest":1,"slug":"derek-woollins","display_name":"Derek Woollins","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""},{"term_id":2666,"user_id":11,"is_guest":0,"slug":"guy-lloyd-jones","display_name":"Guy Lloyd-Jones","avatar_url":{"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/10\/Lloyd-Jones_Guy_FRS_2023_07_DSC_9543ed_01.jpg","url2x":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/10\/Lloyd-Jones_Guy_FRS_2023_07_DSC_9543ed_01.jpg"},"0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""},{"term_id":2664,"user_id":9,"is_guest":0,"slug":"pedro-heloued-ac-uk","display_name":"Pedro Helou","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/bbedc516e27101a62a1416a6313c39a0c4aba307cb1418c3edb637289c738388?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""},{"term_id":2665,"user_id":10,"is_guest":0,"slug":"andres-garcia-dominguez","display_name":"Andres Garcia Dominguez","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/a37e4b073ed5469b8e123832cba4df3bb3cc8b760ca42118499359af45aa97f2?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/29711","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=29711"}],"version-history":[{"count":262,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/29711\/revisions"}],"predecessor-version":[{"id":30427,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/29711\/revisions\/30427"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=29711"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=29711"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=29711"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=29711"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}