1. Pieces of the Propellane Puzzle
Robynne Kirkpatrick,a Tony Masiello,b Narumol Jariyasopit,a Joseph Nibler,a Art Maki,c Alfons Weber,c and Tom Blakeb
bOregon State University
bPacific Northwest National Laboratory
cNational Institute of Standards and Technology
International Symposium on Molecular Spectroscopy, 2007
I’m Robynne and My group is using high resolution infrared specctroscopy to study this molecule…

2. …with a charge distribution that continues to be a topic of debate!?
1.52 Å
1.57 Å
[1.1.1]Propellane,  
a D3h hydrocarbon… 
…with a charge distribution that continues to be a topic of debate!
This interesting molecule was synth by Wiberg and Walker in 1982 catches the eye
Hedberg’s discovered it was D3h and not D3. Early on, it was called propell’ane, and I still call it propellane
When I should probably call it pro’pellane
Note:
1)Orientation of the four carbons with respect to an axial carbon in combination with:
2)Axial cc dist not so atypical– so what contributes to holding the blasted thing in a cage form?
(Underlying question: What are the factors that contribute to its stability and existence– can be stored in the gas phase at rt)
-Synthesis: Wiberg and Walker, J. Am Chem Soc., 1982, 104,
-Structure: L. and K. Hedberg, J. Am Chem Soc., 1985, 107,

3. Some of the Debate
Messerschmidt and coworkers used x-ray diffraction on a derivative that contains of the propellane skeleton, and found
“…no charge accumulation at the center.”
[Angew Chem, 44,   (2005).]
Ab Initio calculations with small basis sets
(6-31g*) give what could be interpreted as conflicting results on the bonding/antibonding nature of the electrons in the HOMO
[Honneger et al, J Am Chem Soc, 107, 7172 (1985).],
[Sannigrahi and Kar, J Mol Struc; Theochem, 496, 1-17 (2000).]
Honneger and coworkers: (Hanspeter, Edgar, Dailey, and Wibert)
: ionization resulted in a slight decrease in the axial cc distance
(IP = 9.7 eV propellane, 9.3 bicyclobutane (two merged triangles), 9.6 bicyclopentane)
Sannigrahi and Kar: HOMO could not be antibonding or nonbonding using a 6-31g*/6-31g** basis

4. Electron Density: (Arbitrary Units)
What do Ab Initio Calcs Done with a Larger Basis Set Say about the Electron Distribution?
sv through 3 Cs
Some areas of relatively low density
Electron Density: (Arbitrary Units)
What do our Ab Initio Calcs tell us?
(Show physical model of molecule.) Looking at the electron density between an axial and an equatorial carbon, (black line),
We see the electron density is somewhat higher in the region between those carbons when we compared to the light blue regon near the dotted red line. (colors reflect mulptiples of electron denstiy)
From B3LYP/cc-pvtz

5. what is the nature of the Highest Occupied MO?
For [1.1.1]Propellane,
what is the nature of the Highest Occupied MO?
Singlet state with
large axial lobes outside the cage
Shows large lobes of the “axial” electrons have room to roam outside the cage
From B3LYP/cc-pvtz

6. What additional information can we learn about Propellane from results of high resolution (~0.002cm-1) Rovibrational Experiments?
(Transition slide- just read The question I want to talk about today is what …)

7. High res spectroscopic results 
●Identify | n, J, K, l > states
(No K states previously observed/assigned!)
●Obtain vibration-rotation parameters
● Learn about charge flux (nature of the dipole derivatives)
●High Resolution spectroscopy enables us to identify the K structure, and knowledge of the K structure
Enables us to understand rotation-vibration properties…

8. 1,1-dibromo-2,2-bis(chloromethyl)cyclopropane
Experimental
Synthesize
Protocol: Belzner et al., Chem. Ber. 122, (1989)
LiCH3
1,1-dibromo-2,2-bis(chloromethyl)cyclopropane
What to do first– well, I was excited to study this molecule so when our group decided to study propellane, I looked and and looked looked (ha ha) online four commerically avialable sources of propellane…and I didn’t find any. This meant I had to revisit my organic chemistry techniques. Tony Masiello and I synthesized propellane at pnnl with a very gracious dr tim huber
We recorded a number of spectra using varying conditions and here is the Bruker that gives such amazing resolution.
Record Spectra
0.5-2 Torr, K, 352 scans averaged,
Bruker FT120/125

9. FTIR Spectrometers at PNNL
Bruker IFS 120/125HR
HR Mirror:
moves 6 m! ,
Here is one of the FTIR spectrometers we use at PNNL.
At this amazing resolution we can see…
I’m going to first show a couple of bands re took spectra of to illustrate what we can see
Resolution
~ cm-1
What Can We See at this resolution?

10. n14 // Band 0.06 vs 0.002 cm-1 Resolution P37 P37 P37 P37
Example of a what we can see
Dotted line represents what would have been a single line if spectra were recorded at the res used in the previous study.
with this parallel band Nu14 H’s moving along the z axis
s w w s C3 axis

11. n10  Band 0.06 vs 0.002 cm-1 Resolution Q0
Here is a perpenduclar band I studied. At the current res we can clearly see the s w s pattern that establishes the molecule has a horizontal plane of symm

12. n15 // Band n15 Jodd Jeven Classic P, Q, R band shape
 D3h nuclear spin weights:
K=0: Jodd:2; Jeven:1
K0: 24 for K = mod 3; 20 otherwise
Jodd
Jeven
Today I’m going to focus on two other bands.
Two lowest freq. Here is the nu15 band. The nu15 mode– axial carbons move one way and eq methylene gruops move in the opp dir
(SA_2 2 torr, .0015, .2m pathlength, -10 degr C, bruker120)
We can see evidence of the nuclear spin statistics in the intensities.
Let’s look at an expanded view of a lower frequency region of this band at the J=62 K stack of the P br
This is all the way out at 575 wavenumbers!!...
cm-1

13. n15 Parallel Band Experiment Calculated cm-1
(The four peaks in the box would have been unresolved at 0.06.) This experiment was done at 0.25 torr, 12.8m pathlenth (white cell), 296K, bruker 125,
We have been able to make assignments at high levels of J and K. The calculated intensities
Match quite well…
What information do we get from fitting the lines?
next slide (intensities good transition, # of lines assigned…)
cm-1

14. ●Calculated intensities quite good
n15 // Band
●Calculated intensities quite good
●1746 transitions assigned
●n15 = (2) cm-1
Previous work cm-1 (Wiberg et al, 1985)
This work, G03 B3LYP/cc-pVTZ Anharm, cm-1
●Rotational parameters for the Ground state and n15 well-determined
We fitted close to 2,000 transitions…
Interesting that the ab initio value was quite a bit off from the expt’l value…
What else can we get?...

15. Delta C matches quite nicely,
Delta D’s well determined…something we cannot get from gaussian
This was the lowest freq // band, let’s look at a perp band located about 90 wavenumbers lower

16. n12  Band n12 (E′) Intensity perturbation!! vs. 500 520 560 540 cm-1
This parallel band that is about 90 wavenumbers away is pretty interesting…
What’s going on here?!!
A bit of a challenge to make some assignments
Let’s get at what’s causing this band to be such an odd shape and see if we can fit this band
cm-1

17. Likely Perturbation Source:
z12,15 Coriolis Interaction ●
 Yes!
● Are the energy levels close?  Yes!
Guess a Coriolis interaction…We know if we rotate an I’ representation…we get
A repres that transforms as a rot species
Relatively close energy levels– about 90 cm-1
ycoupled = ay12+ + by15 + cy12–

18. Coriolis Coupling Operator:
Q = +/- operator for n15
P’s = +/- ops. for n12
J’s = +/- ops. for rotational angular momentum (molecule rotating frame)
To do the fit, weTo do this, we made preliminary assignments and used these energy relationships. We assumed a negative Zeta…(next slide)
 Nonvanishing matrix elements:
±2½(Bzy)[J(J+1) – K(K±1)]½ DK = ±1, Dl = ±1

19. For Frequency Fit, Estimate - zy
Use Normal Coordinate Components (fromB3LYP/cc-pvtz) 
We used Gaussian to get an estimate of zeta. =

20. Q15 (A2’’) ●Yellow Arrow = Dipole Derivative
We used these estimates of normal coords given by gaussian b3lyp/cc-pvtz
Atoms grouped together so we can easily see what moves as a group
●Yellow Arrow = Dipole Derivative
● Black Arrow = Displacement Vector

21. Q12 (E′)
These atoms (colored) move as a group…

22. Frequency Fit ●2244 n12 lines + 1746 n15 used
●Fitting of Energy Parameters Good
n12 = (2)cm-1
G03 B3LYP/cc-pVTZ pair: and 536.2
Ave. = 531.7
(previous work, 529, Wiberg et al)
Here are some of the results of the frequency fitting of n12.
(okay to list the 529?)
Things are looking good, we made assignments…results are these
Let’s look at the vibrot params

23. n12 Rotation-Vibration Parameters
For the vibrational parameters, zeta appears to agree quite well with ab initio calculations
And the ground state params determined using 15 lines didn’t change within our uncertainties!! Wow-
Let’s see how extensive the energetic coupling is

24. Extent of the z12,15 Coupling for
ycoupled = ay12+ + by15 + cy12–
b = 0.073
0.5% n15
Nu 12 states are nearly all nu12 in composition so let’s calculate the intensities
b = 0.109
1.1% n15
 Relatively small amount of n15 in vector composition

25. But the Intensities are Off! Intensities scaled to unperturbed lines
Expt
Calc intensity if no perturbation
cm-1
Intensities scaled to unperturbed lines
Hmmm!
R branch is nearly covered up, and P branch is way high.
Note scale to unpert J=K for delta J and delta K =-1 cannot couple to nu 15 since
Their entire rotational angular momentum is due to rotation around the z axis rather than the x or y axes!
Well, at least the pP lines aren’t too bad! Now to try to fix this…

26. [DiLauro and Mills, J Mol Struc; Theochem, 21, 386-413 (1966).]
Assume Icoupled ~
|m′1212+ + m′15  15 + m′12  12– |2
Where gi is the product of the coupling coefficient, Boltzmann factor, spin weight, frequency, and
Assume this model since intensities are…
[DiLauro and Mills, J Mol Struc; Theochem, 21, (1966).]

27. Intensity Fit for Coupled n12, n15
●Use a least squares regression on intensities to fit the dipole derivative ratio
●701 isolated lines used
●Used ”One side” transitions (pP and rR)
●K > 4
We did an intensity fit—
Used 701 lines, chose all the isolated lines and used the lines that would have been the most intense
In a normal perp branch

28. Ab Initio value from B3LYP/cc-pVTZ is
Results
R^2 is okay, results from ab initio rather consistent
(ab initio just uses dip der sqare to get the int listed)
Ab Initio value from B3LYP/cc-pVTZ is
|m’15/m’12| = 28.9

29. n12  Band Expt Calc intensity m’15/m’12 = 35.2 using z negative
Calc No Coupling
Ahh. That’s better. Look at these individual lines. Note the pink is with no coupling– Wow! What a change!
cm-1

30. Discussion of the Intensities
●n15 a high dipole derivative relative to n12 --most n15 band lines off scale relative to n12
● n15 oscillation associated with considerable charge flux
● Effective dipole derivative of
n15 has a very small
projection onto
the x-y plane if
n12 is excited
n15
A bit of a challenge to use nu15 lines in the dip der ratio sit
Clear that nu 15 assoc with major charge flux
And, if nu 12 and 15 are both on, nu 15 has a slightly off axis component

31. e- density slice through sv and 3 Cs
Large dipole derivative associated with n15  Perhaps the relative axial electron distribution outside the depleted region is significant, and it moves with each axial C during a n15 oscillation
HOMO
e- density slice through sv and 3 Cs
Can we reconcile or relate our experimental results to the questions posed about propellane at the beginning of the
Presentation?
It appears as though the electron dist outside the cage is significant…
In summary…

32. High resolution studies of propellane 
Summary
High resolution studies of propellane 
Accurate vibration-rotation parameters determined and in compared w/ B3LYP/cc-pVTZ anharmonic calcs
 Coriolis coupling found between n12 and n15; dipole derivatives assessed and compared favorably with ab initio calcs
Charge densities and charge flux studied
using B3LYP/cc-pVTZ
Don’t say this