Intricate Conformational Tunneling in Carbonic Acid Monomethyl Ester

Transcription

1 Supplementary Information for Intricate Conformational Tunneling in Carbonic Acid Monomethyl Ester Michael M. Linden, a Jan Philipp Wagner, a Bastian Bernhardt, a Marcus A. Bartlett, b Wesley D. Allen, b * and Peter R. Schreiner a * a Institute of Organic Chemistry, Justus-Liebig University, Heinrich-Buff-Ring 17, Giessen, Germany b Center for Computational Quantum Chemistry and Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA Table of Contents 1. Experimental Methods... S2 2. Procedure for Kinetic Analysis (Table S1)... S3 3. Time Evolution and Kinetic Fits of Conformer Populations (Figures S1-S18)... S4 4. Summary of WKB Tunneling Analysis (Table S2)... S22 5. Cartesian Coordinates and Energies of Geometric Structures... S23 6. Experimental IR Spectra S25 S1

2 Experimental Methods For all matrix-isolation experiments an APD Cryogenics closed-cycle refrigerator system (HC-2 compressor, CS 202 coldhead) was used. The temperature was monitored by a Leybold LTC 60 Si-diode temperature controller. For experiments at 3 K, a cryostat from Sumitomo was employed, which is a combination of an F-70 compressor unit and an RDK 408D2 closed-cycle refrigerator. In order to be suitable for IR measurements, a CsI window was attached to the cold fingers of the cryostats, and KBr windows were used for the outer mantle. High-vacuum flash pyrolysis (HVFP) was performed with a small home-built watercooled furnace that is directly connected to the vacuum shroud. The pyrolysis zone was equipped with a resistively heated, completely empty quartz tube (inner diameter 8 mm, length of heating zone 50 mm). The temperature was controlled by a Ni/CrNi thermocouple equipped with a Voltcraft K204 Digitales/Voltcraft LAP-1363 with 25.6 V and 1.10 A. For deposition in the matrix-isolation experiments, gaseous mixtures of t butyl-methylcarbonate in about 1000-fold excess noble gas were prepared in a 2 L storage glass balloon. The gas mixture was pyrolyzed at a temperature of C typically for 2 h with consumption of ca. 60 mbar. Broadband NIR irradiation of the deposited samples was carried out with a high-pressure mercury lamp (HBO 200 Osram or SP200) in combination with a RG850 longpass filter. IR spectra were recorded with a Bruker Vertex 70 FTIR spectrometer, or alternatively with a Bruker IFS55 spectrometer (resolution 0.7 cm 1, 50 scans collected in one measurement). During the kinetic measurements, a long-pass IR filter (cutting off all wavelengths below 4.5 µm, LOT Oriel, 4.50 ILP-25) was used to prevent unwanted photochemistry induced by the globar; in addition, the matrix apparatus was not moved in order to prevent errors arising from different thicknesses of the deposited matrices. The time between two measurements was 1 h. S2

3 Procedure for Kinetic Analysis Experimental kinetic data measured from the matrix-isolation IR bands tabulated and characterized in Table S1 were selected for the analysis of conformational tunneling in 1. Band intensities were determined by numerical integration over the ranges given in the table. Baselines were set by the absorptions at the endpoints of the ranges. The bands cannot be monitored long enough to closely reach the asymptotes. Moreover, the area under each 1ct band will not decay to zero at infinite time if constant absorptions from contaminants or frozen sites are present. The measured intensity Ii,j(t) of each band j of species i was thus adjusted by a time-independent shift si,j before fitting the temporal profiles. These shifts were determined by minimizing the quantity I S i = i, j (t m ) s i, j I (t ) s i,k m i,k I i, j (0) s i, j I i,k (0) s, j<k m i,k where the sums run over all times tm and all pairs of bands (j,k) for which measurements were made for species i. This approach produced a remarkable consistency of the kinetic data from the various bands of each conformer. The relative intensities from all bands of a given species were averaged for each time tm to arrive at the final data set for fitting the kinetics. Plots of the data and fits are shown in Figures S1-S18. 2 Table S1. Infrared bands a used for kinetic analysis of conformational tunneling in carbonic acid monomethyl ester (1) A1, Ar(3 K) 1ct( cm 1 ), 1ct( cm 1 ), 1ct( cm 1 ), 1ct ( cm 1 ) A2, Ar(7.5 K); A3, Ar(12.5 K); A4, Ar(12.5 K); A5, Ar(17.5 K); A6, Ar(20 K) 1ct( cm 1 ), 1ct( cm 1 ), 1ct ( cm 1 ) A7, Ne(3 K) 1ct( cm 1 ), 1ct( cm 1 ), 1ct( cm 1 ) A8, -CD 3, Ar(3 K) 1ct( cm 1 ), 1ct( cm 1 ) A9, -CD 3, Ar(12.5 K) 1ct( cm 1 ), 1ct( cm 1 ), 1ct( cm 1 ) A10, -CD 3, Ar(20 K) 1ct( cm 1 ), 1ct( cm 1 ), 1ct( cm 1 ), 1ct( cm 1 ) B1-B4, Ar(12.5, 15, 17.5, 20 K) 1ct( cm 1 ), 1ct( cm 1, 1 static), 1ct( cm 1 ), 1ct( cm 1 ), 1ct ( cm 1, 2 static), 1cc( cm 1 )(omitted for 12.5 K); 1cc( cm 1, 2 shoulders)(omitted for 17.5 K), 1cc( cm 1, 1 shoulder); 1cc( cm 1, 1 shoulder), 1cc( cm 1, 2 shoulders) a (Shoulder, static) refer to features additional to the main peak that are time (dependent, independent). S3

4 Figures S1-S18. Time evolution and kinetic fits of the relative populations of the conformers of 1 in various matrices. Figure S1. Experiment A1: Ar (3 K) Blue curve: monoexponential, τ = h Red curve: biexponential, τ slow= 17.1 h (69.4%), τ fast= 5.9 h (30.6%) S4

5 Figure S2. Experiment A2: Ar (7.5 K) Blue curve: monoexponential, τ = h Red curve: biexponential, τ slow= 23.2 h (45.7%), τ fast= 6.6 h (54.3%) S5

6 Figure S3. Experiment A3: Ar (12.5 K) Blue curve: monoexponential, τ = h Red curve: biexponential attempt S6

7 Figure S4. Experiment A4: Ar (12.5 K) Blue curve: monoexponential, τ = h S7

8 Figure S5. Experiment A5: Ar (17.5 K) Blue curve: monoexponential, τ = h S8

9 Figure S6. Experiment A6: Ar (20 K) Blue curve: monoexponential, τ = h S9

10 Figure S7. Experiment A7: Ne (3 K) Blue curve: monoexponential, τ = h Red curve: biexponential, τ slow= 50.4 h (51.9%), τ fast= 12.5 h (48.1%) S10

11 Figure S8. Experiment A8: -CD3, Ar (3 K) Blue curve: monoexponential, τ = h Red curve: biexponential, τ slow= 65.2 h (68.3%), τ fast= 13.2 h (31.7%) S11

12 Figure S9. Experiment A9: -CD3, Ar (12.5 K) Blue curve: monoexponential, τ = h Red curve: biexponential, τ slow= 42.7 h (89.4%), τ fast= 8.2 h (10.6%) S12

13 Figure S10. Experiment A9: -CD3, Ar (20 K) Blue curve: monoexponential, τ = h Red curve: biexponential, τ slow= 43.3 h (88.7%), τ fast= 6.3 h (11.3%) S13

14 Figure S11. Experiment B1: Ar (12.5 K) Simultaneous fit to 1ct(red) and 1cc(blue) Biexponential curves, τ slow = 22.6 h (57.8%), τ fast = 7.0 h (44.2%),τ eff = 12.8 h, γ = 0.79 Precise fitting of the 1cc curve (only) requires the addition of small 2 t/τ f γ f conformer with τ f = 4.7 h and γ f = feeder term in eq (2) for this S14

15 Figure S12. Experiment B1: Ar (12.5 K) Fit without 1cc feeder Biexponential curves, τ slow = 23.8 h (54.6%), τ fast = 6.8 h (45.4%),τ eff = 12.7 h, γ = 0.83 S15

16 Figure S13. Experiment B2: Ar (15 K) Simultaneous fit to 1ct(red) and 1cc(blue) Biexponential curves, τ slow = 24.2 h (54.1%), τ fast = 6.8 h (45.9%),τ eff = 12.8 h, γ = 0.55 Precise fitting of the 1cc curve (only) requires the addition of small 2 t/τ f γ f conformer with τ f = 1.7 h and γ f = feeder term in eq (2) for this S16

17 Figure S14. Experiment B2: Ar (15 K) Fit without 1cc feeder Biexponential curves, τ slow = 20.1 h (67.4%), τ fast = 5.7 h (32.6%),τ eff = 12.9 h, γ = 0.58 S17

18 Figure S15. Experiment B3: Ar (17.5 K) Simultaneous fit to 1ct(red) and 1cc(blue) Monoexponential curves, τ = h, γ = 0.43 Precise fitting of the 1cc curve (only) requires the addition of small 2 t/τ f γ f conformer with τ f = 3.3 h and γ f = feeder term in eq (2) for this S18

19 Figure S16. Experiment B3: Ar (17.5 K) Fit without 1cc feeder Monoexponential curves, τ = h, γ = 0.60 S19

20 Figure S17. Experiment B4: Ar (20 K) Simultaneous fit to 1ct(red) and 1cc(blue) Monoexponential curves, τ = h, γ = 0.58 Precise fitting of the 1cc curve (only) requires the addition of small 2 t/τ f γ f conformer with τ f = 3.8 h and γ f = feeder term in eq (2) for this S20

21 Figure S18. Experiment B4: Ar (20 K) Fit without 1cc feeder Monoexponential curves, τ = h, γ = 0.72 S21

22 Summary of the Tunneling Analyses Table S2. Tunneling analysis of carbonic acid, 1, and [D 3 ]-1 at the CCSD(T)/cc-pVQZ//MP2/aug-cc-pVTZ level of theory Tunneling parameters Carbonic acid 1 [D 3 ]-1 Collision energy (ε, kcal mol 1 ) Collision frequency (ω 0, cm 1 ) Effective barrier (kcal mol 1 ) Turning points [(s 1, s 2 ), a.u.] ( 2.06,1.81) ( 2.08,1.87) ( 2.08,1.87) Effective barrier frequency (cm 1 ) 558i 542i 542i Barrier penetration integral (θ) Transmission probability κ(wkb) Transmission probability κ(zct) Transmission probability κ(sct) Tunneling half-life a τ(wkb) 8.7 min 12.9 min 12.7 min Tunneling half-life a τ(zct) 12.8 min 12.6 min Tunneling half-life a τ(sct) 0.29 min 0.30 min a The computed half-life was divided by a factor of two due to the degeneracy of the reaction path. S22

23 Cartesian Coordinates, Electronic and Zero-Point Energies Table S3. Cartesian coordinates (in Å) of the MP2/aug-cc-pVTZ optimized structures, their electronic and zero-point vibrational energies (in E h ) at the same level, and the CCSD(T)/cc-pVQZ single point energy cis,cis-carbonic acid X Y Z C O O O H H E(MP2) = ; ZPVE(MP2) = cis,trans-carbonic acid X Y Z C O O O H H E(MP2) = ; ZPVE(MP2) = ; E[CCSD(T)] = carbonic acid TS X Y Z C O O O H H E(MP2) = ; ZPVE(MP2) = ; E[CCSD(T)] = S23

24 1cc X Y Z C O O O H C H H H E(MP2) = ; ZPVE(MP2, -CH 3 ) = ; ZPVE(MP2, -CD 3 )= ct X Y Z C O O O H C H H H E(MP2) = ; ZPVE(MP2, -CH 3 ) = ; ZPVE(MP2, CD 3 ) = E[CCSD(T)] = TS X Y Z C O O O H C H H H E(MP2) = ; ZPVE(MP2, -CH 3 ) = ; ZPVE(MP2, CD 3 ) = E[CCSD(T)] = S24

25 Experimental IR Spectra Figure S19. Experiment A1: Ar (3 K) IR spectrum of carbonic acid monomethyl ester (1) directly after deposition in an argon matrix. Bands that were used for our kinetic analysis are marked with an asterisk (see also Table S1). S25

26 Figure S20. Experiment A8: Ar (3 K) IR spectrum of deuterated carbonic acid monomethyl ester ([D 3]-1) directly after deposition in an argon matrix. Bands that were used for our kinetic analysis are marked with an asterisk (see also Table S1). S26

27 Figure S21. Experiment A7: Ne (3 K) IR spectrum of carbonic acid monomethyl ester (1) directly after deposition in a neon matrix. Bands that were used for our kinetic analysis are marked with an asterisk (see also Table S1). S27