1. Chirped pulse rotational spectroscopy
71st International Symposium on Molecular Spectroscopy WC01
Chirped pulse rotational spectroscopy
of a single thujone+water sample
Zbigniew Kisiel,
Institute of Physics, Polish Academy of Sciences, Warszawa, Poland
Cristobal Perez, Melanie Schnell,
CoCoMol, Max-Planck-Institut fur Struktur und Dynamik der Materie,
Hamburg, Germany

2. Early investigation using Low-resolution Microwave Spectroscopy (LRMW):
Under suitable conditions rotational spectrum collapses to a series of equally spaced lines with spacing equal to B+C
Thujone: B+C =1522.1(5) MHz   = 15o
Isothujone: B+C =1416.8(18) MHz   = 25o
Kisiel + Legon, JACS 100, 8166 (1978)
assumptions based on 3-bicyclo[3.1.0]hexanone, Bevan et al. JACS 100, 8161 (1978)

3. Chirped pulse spectrum recorded in Hamburg:
Praha2008
Chirped pulse spectrum recorded in Hamburg:
-Thujone
Commercial thujone sample:
70% -thujone
10% -thujone (isothujone)
20% unspecified….
Conditions similar to those used in the recent camphor+water study: J.Phys.Chem.Lett. 7, 154 (2016):
He carrier gas, 3.5bar, passed over
1:1 H216O:H218O, then over thujone
gas 4Hz, 8 chirps per gas pulse
1.4M FIDs averaged = 12 hr
Aim: study the natural product monomers + their hydration clusters
-Thujone = Isothujone

4. Visibility of 13C thujone in natural abundance:
Praha2008
Visibility of 13C thujone in natural abundance:
Parent species, 403 ← 302
(Kaiser-Bessel windowing function mandatory)
J = 7 ← 6, Ka = 1 ↔ 0
a- + b-type quartet for thujone-(H2O)2
13C1
13C5
13C3
13C2

5. Visibility of 18O thujone in natural abundance:
Praha2008
thujone+H218O: 532 ← 431
13C6 thujone: 403 ← 302
18O thujone: 413 ← 312

6. Praha2008
Assigned species:
Assignment and analysis carried out using various combinations of AUTOFIT, AABS, JB95, SPFIT/SPCAT and quantum chemistry calculations
-Thujone: parent (23 aR-, 13 bR-, 56 bQ-, 7 cR-, 11 cQ-type transitions)
+ all ten single 13C species + 18O species
-Thujone = Isothujone: parent (also a-, b-, and c-type transitions)
Thujone-II: similar to -Thujone but differing in isopropyl orientation, parent species
Fenchone: parent (also a-, b-, and c-type transitions) + all ten single 13C species
-Thujone + H2O: two isomers and their H218O isotopologues
-Thujone + 2H2O: parent + single and double H218O isotopologues

7. Rotational constants old and new:
Praha2008
THUJONE ISOTHUJONE
this work this work
A /MHz (46) (50)
B /MHz (31) (26)
C /MHz (31) (25)
B+C /MHz (44) (5) (36) (18)
DJ /kHz (63) (37)
DJK /kHz (42) (65)
DK /kHz (22)
dJ /kHz (23) (54)
dK /kHz (14) (35)
Nlines
sigma/kHz

8. Unfortunately thujone has multiple small atomic coordinates:
Praha2008
The r0 structural fit (26 parameters to 36 rotational constants) is very satisfactory but precision is degraded to:
0.009 – Å for r(CC)
0.5 – 1.1° for  (CCC)

9.  Thujone skeletal angles old and new:  1978: 15 expt. 18.4(19)
Praha2008 
1978: 15
expt. 18.4(19)
calc. 19.6 
1978: 66.9
expt. 70.3(12)
calc. 70.8 
ISOTHUJONE:
Calc 21.4
expt. 62.7(22)
calc. 61.6
expt. 85.3(21)
calc. 88.9
expt (22)
calc

10. Fenchone (+ its 13C species) and another thujone isomer:
Praha2008
Fenchone (+ its 13C species) and another thujone isomer:
expt calc.
A /MHz (54)
B /MHz (25)
C /MHz (25)
Thujone-II
Fenchone
expt calc.
A /MHz (28)
B /MHz (32)
C /MHz (32)
Assignment of fenchone was attempted since it is stated to be a significant constituent of most thuja oils.
Fenchone is similar to camphor, and camphor lines have also been seen.
STOP PRESS! Donatella Loru + Maria Sanz from King’s College London have also studied fenchone – see talk WC11

11. Thujone + single water molecule clusters:
Praha2008
Calculated to be the more stable conformer.
This is similar to the situation for camphor-water.
a , b , and c allowed transitions observed

12. Thujone + 2 water molecules cluster:
Praha2008
Thujone + 2 water molecules cluster:
Structure determined from fit to 12 rotational constants for four isotopic species: parent,
two single H218O,
one double H218O
± Å
± Å

13. SUMMARY: A single chirped pulse spectrum recorded in 12 h allowed:
Praha2008
SUMMARY:
A single chirped pulse spectrum recorded in 12 h allowed:
Assignment of rotational spectra and determination of spectroscopic constants for 4 different natural product molecules
Determination of heavy atom backbones of 2 molecules from isotopic species in natural abundance
Assignment of 3 different hydration clusters and parameters of their intermolecular bonds from H218O substitution
Thujone is a natural product with an intriguing connection to human culture:
Thujone  Absinthe  Piołunówka
…mysterious, addictive, and mind- altering drink….
L’Absinthe, by Edgar Degas, 1876 (Wikipedia)