1. The microwave spectroscopy study of 1,2-dimethoxyethane
Weixing Li, Annalisa Vigorito, Camilla Calabrese, Luca Evangelisti*, Laura B. Favero, Assimo Maris, Sonia Melandri*
Supervisor: Prof. Sonia Melandri
Università di Bologna

2. Why we study… Some interesting facts about 1,2-dimethoxyethane

3. Rich configuration variations
Trans (T)
Gauche (G)
Gauche’ (G’)
Three bond rotations generate 33 possible rotamers giving 10 non-equivalent molecular configurations

4. Two rotors with internal rotation
Internal rotations of the two CH3 rotors can split the spectra.
0,0
0,±1
±1,0
± 1, ± 1
± 1, ∓1
σ1= -1,0,1
σ2= -1,0,1

5. How we measure… Two kinds of MW spectrometers were used

6. Free-jet Absorption Spectrometer
Millimeter-Wave Stark modulated Free-Jet Absorption Spectrometer
BUILT in 1993 by Prof. P. FAVERO, Prof. W. CAMINATI and Prof. S. MELANDRI
on the model of the MONASH UNIVERSITY one.
FREE –JET EXPANSION
Tvib K (depends on the vibrational gap)
Trot 1-10 K (Boltzmann distribution)
SWEEP RATE
1 GHz per hour
FREQUENCY RANGE
54-118GHz
SENSITIVITY
RESOLUTION
@ Bologna
cm-1
kHz
Camilla Calabrese

7. Fourier Transform Microwave Spectrometer
Covering range: 6.5 ─18 GHz
Resolution: 5 kHz
Sensitivity: cm-1
Pressure: 2 bar → ~10-5 mbar
Temperature: 1 K
Caminati, W; Evangelisti, L; Feng, G; Giuliano, B. M.; Gou, Q; Melandri, S; Grabow, J-U, PCCP, 2016, 18, –

8. Energy schematic diagram of the conformers transforming
cm-1
1500 θ1 θ1 θ3 θ1 θ2 θ1
GTG
GTG’
1000 θ3 θ1 θ2
GGG’
TGG θ3
TTG
GGG
500 θ3
9 non-equivalent conformers
TGT
TGG’
TTT
Calculated at MP2/ G** level

9. Stuctures and energies with and without zero-point energy
Calculated at MP2/ G**
B3LYP/ G**
TGT conformer is the most abundant conformer in liquid and crystalline. a
TGG’ conformer is the most abundant conformer in gas phase. a
TTT conformer is the lowest energy conformer. a
Degeneracy: TTT : 1
TGT : 2
TGG’ : 4
aG.D Smith et. al J. Am. Chem. SOC.1995,117,

10. Predicted spectroscopic parameters of three most stable conformers
Calculated at MP2/ G** level

11. Example spectra of two assigned conformers
Free-jet Absorption MW
FTMW

12. Spectroscopic parameters of two assigned conformers
MP2
10.0
6.9
9.7
10.0
6.9
9.7
XIAM: H.Hartwig and H.Dreizler, Z. Naturforsch 51a, (1996).
ERHAM: P. Groner, J. Chem. Phys.107, (1997).

13. V3 comparison of different molecules
1) Esters with –OCH3 V3 below 6 kJ/mol
V3=6.58 kJ/mol
V3=13.2 kJ/mol
2) Ethers with –OCH3 V3 between 6-11 kJ/mol
3)–OCH3 takes part in an intra-HB V3 around 13 kJ/mol

14. Rotational parameters of 13C substituted species

15. Kraitchman’s coordinates of 13C substituted species compared with calculation results (MP2/ G**) C1 C6 C1 C6 C3 C4 C3 C4

16. Relative population of two conformers in molecular beam’ ’ ’ ’ ’
g = gTGG’/gTGT = 4/2
NTGG’/NTGT = 2.1/ vs /1
Experiment ab initio

17. To Conclude… Two conformers were assigned in rotational spectra.
All the 13C substituted species were identified.
V3 barrier of each -OCH3 rotor in both conformers were measured, and intra- HB plays an important role.

18. Acknowledgements Prof. Sonia Melandri Prof. Walther Caminati
Dr. Assimo Maris
Dr. Luca Evangelisti
Dr. Laura Favero
Dr. Camilla Calabrese
Dr. Annalisa Vigorito
Dr. Lorenzo Spada
Chinese Scholarship Council