1. Observation of Trans-Ethanol and
Gauche-Ethanol Complexes with Benzene Using Matrix Isolation Infrared Spectroscopy
Jay C. Amicangelo, Matthew J. Silbaugh,
Tracy A. Jones, Benjamin C. Mull

2. CH3OH-C6H6 Complex
1:1 H- complex observed in low temperature argon and nitrogen matrices
2013 ISMS TE08; ISMS RJ14
CH3OH+C6H6
CH3OH
C6H6
20 K Ar Matrix
17 K N2 Matrix
1:1 complex
1:1 complex
O–H Frequency Shifts
expt Ar = cm-1
expt N2 = cm-1
MP2 = cm-1
MP2/aug-cc-pVDZ
16.0 kJ/mol
2.42 Å

3. C2H5OH Rotation of OH relative to CH3 → 2 conformers
Trans (180°) & gauche (60°)
MP2/aug-cc-pVDZ relaxed potential energy scan
gauche
trans
gauche
trans
ΔEg-t (MP2/aDZ) = 1.1 kJ/mol
ΔEg-t (B3LYP/aDZ) = 0.78 kJ/mol
ΔEg-t (Exp, MW) = 0.49 kJ/mol (J. Chem. Phys. 1980, 76, 4300)
ΔEg-t (Exp, far-IR) = 0.50 kJ/mol (J. Mol. Struct. 1989, 238, 195)
ΔEg-t (Exp, Xe soln-IR) = 0.74 kJ/mol (J. Mol. Struct. 2011, 985, 202)

4. Gas Phase IR Spectra of C2H5OH
MP2/aug-cc-pVDZ
trans
gauche
J. Mol. Spect. 2011, 985, 202

5. Matrix Isolation IR Spectra of C2H5OH
Nitrogen vs argon matrices
1:1800 C2H5OH:M
Nitrogen Matrix
Argon Matrix
B3LYP/aug-cc-pVDZ
trans
30 K
36 K
28 K
gauche
8 K
8 K
Nitrogen matrix  both trans and gauche observed
trans → gauche at 30 K
Argon matrix  only trans observed
J. Phys. Chem. A 1998, 102, 5789

6. Matrix Isolation Infrared Spectroscopy Experiments
C2H5OH + C6H6 co-depositions in Ar & N2 matrices
K deposition; 4 – 6 mmol/hr; hours; 0.5 cm-1
1: :1600 S:M ratios
Annealing: Ar → 35 K & N2 → 30 K
Isotopic experiments: C2D5OD + C6H6
C6H6:Ar/N2
C2H5OH:Ar/N2

7. MP2/aug-cc-pVDZ Optimized Structures
C2H5OH-C6H6 Complex Calculations
B3LYP/aug-cc-pVDZ & MP2/aug-cc-pVDZ
Optimization & BSSE corrected energies (kJ/mol)
MP2/aug-cc-pVDZ Optimized Structures
2.41 Å
2.41 Å
2.38 Å
2.37 Å
trans eclipsed
trans staggered
gauche eclipsed
gauche staggered
Method
Trans eclipsed
Trans staggered
Gauche eclipsed
Gauche staggered
B3LYP/aDZ
5.2
5.3
5.1
MP2/aDZ
16.3
17.6
17.5

8. gauche barrier ≈ 0.11 kJ/mol
C2H5OH-C6H6 Rigid Potential Energy Scan
MP2/aug-cc-pVDZ; C6H6 rotation & C2H5OH fixed
trans eclipsed
gauche eclipsed
trans barrier ≈ 0.06 kJ/mol
gauche barrier ≈ 0.11 kJ/mol
kT = 0.14 – 0.17 kJ/mol at 17 – 20 K

9. C2H5OH-C6H6 Complex Calculations MP2/aug-cc-pVDZ frequency analysis
48.8 cm-1
49.5 cm-1
trans staggered
trans eclipsed
Δt-g complex ≈ 20 cm-1
trans monomer
57.2 cm-1
58.0 cm-1
gauche staggered
gauche eclipsed
gauche monomer

10. C2H5OH-C6H6 Complex Calculations B3LYP/aug-cc-pVDZ frequency analysis
34.2 cm-1
34.8 cm-1
trans eclipsed
trans staggered
Δt-g complex ≈ 18 cm-1
trans monomer
33.2 cm-1
33.5 cm-1
gauche eclipsed
gauche staggered
gauche monomer

11. C2H5OH:Ar vs C2H5OH:N2 Matrix Spectra
Ar  1:1600, 20 K deposition & 35 K anneal
N2  1:3200, 17 K deposition & 30 K anneal
Δt-g (O−H) = 3.9 cm-1
N2 30 K
trans
gauche
N2 17 K
Ar 35 K
trans
Ar 20 K
N2 30 K
N2  trans & gauche observed
trans → gauche at 30 K
gauche
trans
trans
N2 17 K
Ar  only trans observed
Ar 35 K
trans
trans
Ar 20 K

12. C2H5OH:N2 + C6H6:N2 Concentration Study
1:200 – 1:1600 S:M ratios; O−H stretching region
17 K co-depositions
gauche complex
C6H6
trans complex ?
1:200
1:400
1:800
1:1600
1:3200 monomer
Δt-g (O−H) = 3.9 cm-1
17 K co-depositions +
30 K anneal
higher complex
gauche complex
trans complex
C6H6
1:200 ?
1:400
1:800
1:1600
1:3200 monomer

13. C2H5OH:N2 + C6H6:N2 Isotopic Spectra
C2H5OH/C2D5OD; O−H/O−D stretching region
1:1600 C2H5OH + 1:1600 C6H6
1:800 C2D5OD + 1:800 C6H6
17 K
17 K
trans complex
gauche complex
E + B
gauche complex
E + B E
trans complex E B B
30 K
30 K
gauche complex
gauche complex
E + B
trans complex E
E + B
trans complex E B B

14. C2H5OH:Ar + C6H6:Ar Concentration Study
1:100 – 1:800 S:M ratios; O−H stretching region
trans complex
20 K co-depositions
higher complex
1:100
1:200
1:400
1:800
1:1600 monomer
trans complex
20 K co-depositions +
35 K anneal
higher complexes
1:100
1:200
1:400
1:800
1:1600 monomer

15. C2H5OH:Ar + C6H6:Ar Isotopic Spectra
C2H5OH/C2D5OD; O−H/O−D stretching region
1:800 C2H5OH + 1:800 C6H6
1:800 C2D5OD + 1:800 C6H6
trans complex
20 K
trans complex
20 K
E + B
E + B E E B B
trans complex
35 K
trans complex
35 K
E + B
E + B E E B B

16. Nitrogen Matrix Spectra
Complex Frequencies & Shifts (cm-1)
B3LYP/aug-cc-pVDZ; freqs scaled by
MP2/aug-cc-pVDZ; freqs scaled by
Nitrogen Matrix Spectra
Conformer
Monomer
Complex
Shift
experiment
trans
3652.8
3603.4
−49.4
B3LYP/aDZ
trans ecl
3717.4
3684.2
−33.2
MP2/aDZ
3682.1
3634.5
−47.6
gauche
3648.9
3599.5
gauche ecl
3699.1
3666.8
−32.3
3670.9
3615.1
−55.8
Argon Matrix Spectra
Conformer
Monomer
Complex
Shift
experiment
trans
3655.6
3612.3
−43.3
B3LYP/aDZ
trans ecl
3717.4
3684.2
−33.2
MP2/aDZ
3682.1
3634.5
−47.6

17. Summary
Calculations predict weakly bound complexes for trans and gauche C2H5OH with C6H6
B3LYP ≈ 5.1 – 5.3 kJ/mol & MP2 ≈ 16.3 – 17.6 kJ/mol
O-H freq shifts ≈ – 30 cm-1(B3LYP) & ≈ – 50 cm-1 (MP2)
Co-deposition of C2H5OH (& C2D5OD) with C6H6 in N2 & Ar matrices performed
N2 Matrix
O-H peaks observed for gauche & trans complexes
Ar Matrix
O-H peaks observed for only trans complex
MP2 freq shifts compare more favorably with expt