1. Microwave Measurements of Cyclopropanecarboxylic Acid and its Doubly Hydrogen Bonded Dimer with Formic Acid
Aaron M. Pejlovas, Kexin Li, Dr. Stephen G. Kukolich
Dr. Wei Lin (University of Texas Rio Grande Valley)
ISMS June 2016

2. Earlier Work

3. Conformers of CPCA
B3LYP/aug-cc-pVQZ predicted difference in E of ~ 0.92 kcal/mol (~ 320 cm-1)

4. Ground State Conformation of CPCA
Microwave measurements at 5-15 GHz using pulsed beam FT microwave spectrometer
Heat sample to ~50 °C
Parent, –OD isotopologue, all unique singly substituted 13C isotopologue
Natural abundance (except –OD, synthesized through exchange rxn w/ MeOD)

5. 13C(3&6) 13C(9) 13C(1) -OD Parent A/MHz 7563.3591(16) 7624.9982(19)
13C(3&6)
13C(9)
13C(1)
-OD
Parent
A/MHz
(16)
(19)
(38)
(64)
(17)
B/MHz
(90)
(19)
(22)
(14)
(8)
C/MHZ
(96)
(19)
(28)
(14)
(5)
ΔJ/kHz
0.3845*
ΔJK/kHz
3.087*
ΔK/kHz
-0.447*
δJ/kHz * *
φJ/Hz * N 6 5 9 16
σ/kHz 2 3
*Marstokk, K. -M.; Mollendal, H.; Samdal, S. Acta Chemica Scandinavica 1991, 45,

6. Excited State Conformer
Microwave measurements at 5-11 GHz (PBFT)
Previously searched for at GHz, but not observed1
Only parent isotopologue measured
Transitions observed at RT
1Marstokk, K. -M.; Mollendal, H.; Samdal, S. Acta Chemica Scandinavica 1991, 45,

7. Experiment B3LYP/aug-cc-pVQZ MP2/6-311+G**1 A/MHz 7452.3132(57)
Experiment
B3LYP/aug-cc-pVQZ
MP2/6-311+G**1
A/MHz
(57)
7451
B/MHz
(43)
2786
C/MHZ
(40)
2411
DJ/kHz
0.29(53)
DJK/kHz
2.5(12) N 10
σ/kHz 5
1Marstokk, K. -M.; Mollendal, H.; Samdal, S. Acta Chemica Scandinavica 1991, 45,

8. 101 to 000 transitions, recorded after 230 pulsed-beam cycles.
Appeared to be similar intensity as 13C signals of ground state conformer

9. CPCA – FA Dimer
Measured transitions from parent, all unique singly substituted 13C (natural abundance), and D-FA (purchased)
Sample of FA cooled to -8 °C, CPCA and valve at 60 °C

10. Parent
13C(16)
13C(3&6)
13C(1)
13C(9)
D(17)
A/MHz
(16)
(21)
(25)
(22)
(37)
(66)
B/MHz
(14)
(16)
(18)
(17)
(30)
(32)
C/MHz
(23)
(17)
(20)
(19)
(33)
(12)
ΔJ/kHz
0.0499(16)
0.0499*
ΔJK/kHz
0.108(14)
0.108* N 31 7
σ/kHz 2 1 6
Type
B97D/aug-cc-pVTZ
MP2/aug-cc-pVTZ
Parent (exp.)
A/MHz
B/MHz
732.32
747.56
740.58
C/MHz
652.25
663.19
658.57
µa(Debye)
1.7
1.4
µb(Debye)
0.2
µc(Debye)
0.0

11. CPCA – FA Dimer No concerted proton tunneling observed
Singlet a- and b-type transitions
Structure fit for dimer to determine H-bond distances
Interatomic Distance
Microwave Fit Value
Calculated (MP2) Value
r(H12-O14)
1.36
1.67
r(O11-H13)
2.25
1.62
COM Separation
4.11
4.09

12. CPCA-FA Dimer

13. Excited Dimer Conformer?
B97D/aug-cc-pVTZ predicted E separation of 210 cm-1
Did not observe excited conformer of dimer after extensive searches

14. Acknowledgements Dr. Stephen Kukolich
Dr. Wei Lin (University of Texas Rio Grande Valley)
Kexin Li
NSF
University of Arizona