1. Juliane Heitkämper, John C Mullaney, Nick Walker
Broadband FTMW Spectroscopy of 2-methylimidazole and Complexes with Water and Argon
Chris Medcraft
Juliane Heitkämper, John C Mullaney, Nick Walker
Newcastle University

2. Imidazoles Forms the basis of many biomolecules
Histidine, Guanine, Adenine, Haemoglobin
Imidazole-Based Medicinal Chemistry
Many intermolecular interactions possible
donate or accept H-bond
π-bonding
ion–dipole
cation–π
π–π stacking

3. Imidazole
ChemPhysChem, 2016, 17, 1154 – 1158

4. Newcastle CP-FTMW Spectrometer Two frequency ranges 2-8 GHz 6.5-18 GHz
Hot swappable
Laser Ablation Source
Nanosecond Nd:YAG
20 mJ/pulse
532nm
Brown et. Al., Rev. Sci. Instrum. 79, (2008)

5. Laser Ablation Sources

6. Imidazole ablation products

7. 2-methylimidazole Methyl group may interfere with H-bonding π bonding?
Different dimer structure?

8. Assignment Procedure Internal rotor + 2 nitrogen quadrupoles
A-state lines fit using PGOPHER
Quadrupole coupling constants
Isotopologues  Structure
E-state lines identified from similar intensity and quadrupole structure
Line centres exported to XIAM
V3 Barrier heights

9. Isotopologues Natural abundance 3.5 million FIDs ~60 hours
JKaKc’’ JKaKc’: 212101
13C(5)
15N(1)
13C(2)
15N(3)
13C(9)
13C(4)

10. Isotopologues 212101 13C(5) 13C(2) 15N(3) 13C(9) 13C(4) 15N(1) Parent
A (MHz)
(19)
(34)
(34)
(41)
(30)
(36)
(32)
B (MHz)
(88)
(76)
(78)
(10)
(79)
(10)
(75)
C (MHz)
(66)
(75)
(70)
(92)
(69)
(94)
(75)
DJ (Hz)
83(33)
DJK (kHz)
1.661(79)
DK (MHz)
(47)
(70)
(72)
0.0895(10)
(67)
(74)
(67)
d1 (Hz)
-20.6(78)
d2 (Hz)
-14.5(40)
χaa (MHz)
1.2955(56)
1.301(17)
1.294(20)
1.285(17)
1.297(20)
1.318(20)
χbb-cc (MHz)
4.199(11)
4.191(24)
4.198(24)
4.199(26)
4.169(32)
4.189(25)
1.3891(65)
1.384(19)
1.368(22)
1.454(17)
1.379(22)
1.411(20)
-5.378(11)
-5.401(29)
-5.387(35)
-5.401(31)
-5.346(32)
-5.363(25) N
184 21 48 19 54 56 58 σ
11.9
8.2
11.5
12.9
14.3
12.4
13C(5)
13C(2)
15N(3)
13C(9)
13C(4)
212101
15N(1)

11. Structure rs rm(1) Substitution (rs) and mass weighted (rm(1))
Parameter rs
rm(1)
B3LYP/ aug-cc-pvtz
C(2) C(9)
1.4956(27)
1.4923(18)
1.489 
C(2) N(1)
1.317(31)
1.3367(33)
1.366 
C(2) N(3)
1.333(37)
1.3289(32)
1.314 
C(4) C(5)
1.3653(31)
1.3599(20)
1.364 
N(3) C(4)
1.417(35)
1.3735(36)
1.376 
N(1) C(5)
1.400(13)
1.4026(35)
1.379 
C(9) C(2) N(1)
124.0(30)
124.25(28)
123.42
N(3) C(2) N(1)
113.5(14)
112.04(20)
110.52
N(1) C(5) C(4)
104.93(21)
104.95(13)
105.04
N(3) C(4) C(5)
110.20(47)
(98)
110.43
C(2) N(3) C(4)
106.20
C(9) C(2) N(3)
122.5(31)
123.71(22)
126.05 rs
Pcc = (31) amu Å
rm(1)

12. Internal Rotor JKaKc’’ JKaKc’: 212101 A state E state 38 40 A
Intensity / μV

13. Methyl Rotor fit aug-cc-pvtz A - state XIAM B3LYP-D3 A (MHz)
(19)
(13)
B (MHz)
(88)
(27)
C (MHz)
(66)
(25)
DJ (Hz)
83(33)
---
DJK (kHz)
1.57(13)
12(5)
DK (kHz)
99.27(47)
-79(35)
d1 (Hz)
-20.6(78)
----
d2 (Hz)
-14.5(40)
χaa(N1) (MHz)
1.2955(56)
χbb-cc(N1) (MHz)
4.199(11)
1.3891(65)
-5.378(11)
V3 (cm-1)
(19)
109.3
F0 (GHz)
ε (rad)
2.923(77)
δ (rad)
(36) N
182 41
σ (kHz)
11.5
583
aug-cc-pvtz

14. 4(5)-methylimidazole 378.416 cm-1 Tautomerisation 311.936 cm-1
Brent Harris, PhD Thesis, University of Virginia, 2014.

15. Experimental methyl V3 barrier heights (cm-1)
357.6
imidazole
429.3
pyrrole
thiazole
oxazole
477.7
332.03
34.938
251.6
45.0
105.8
380.5
258.4
isothiazole
thiophene
furan
isooxazole
194.1
62.8
416.2
271.9
Grabow et al. J. Mol. Struct. 2002, 612 (2), 349–356.

16. 2-methylimidazole---argon 2-methylimidazole---H2O
2.48 Å
1.87 Å
162.5º
(44) Å

17. 2.48 Å 3.40934(44) Å 1.87 Å 162.5º 2-methylimidazole---water
2-methylimidazole---argon
Experiment
DFT
A (MHz)
(30)
(46)
B (MHz)
(15)
(42)
C (MHz)
(12)
(75)
DK (MHz)
(50)
(20)
DJK (kHz)
6.583(72)
(99)
42.58
DJ (kHz)
0.443(16)
2.4564(63)
2.224
d2 (kHz)
(16)
-0.42
d1 (kHz)
-0.134(11)
(51)
-0.65
χzz (MHz)
1.232(14)
1.296
(99)
-2.801
χxx-yy (MHz)
4.077(37)
4.239
-0.114(21)
-0.224
(99)
-3.213
1.950(11)
2.25
-0.339(34)
-0.49
4.746(20)
-2.253
σ (kHz)
15.9
18.5 N
172
295

18. 2-methylimidazole---argon 2-methylimidazole---H2O 606505
JKaKc:514505
514505 E A
523413 E A A E
Monomer
Argon
Water
A (MHz)
(13)
(14)
(51)
B (MHz)
(27)
(86)
(30)
C (MHz)
(25)
(12)
(26)
V3 (cm-1)
(19)
(26)
154.08(18)
2-methylimidazole
2-methylimidazole---argon
2-methylimidazole---H2O
606505
16180 MHz
16280 MHz

19. V3 Barrier XIAM V3(cm-1) 2-methylimidazole---H2O
B3LYP-D3/aug-cc-pvtz
XIAM V3(cm-1)
2-methylimidazole---H2O
2-methylimidazole---argon
2-methylimidazole

20. 2-methylimidazole Methyl group might inhibit H-bond formation
Monomer and 13C and 15N isotopologues observed
Water and Argon complexes observed
Methyl group internal rotation

21. Acknowledgements Nick Walker Juliane Heitkämper John Mullaney
Graham Cooper
Dror Bittner