Table 4. Selected Geometric Features of the Alkyl Chlorides, Alkylammonium Ions, and Their Identity SN2 Substitution Transition States (Distances in Angstroms)a.
| alkyl group | d(Cα–Cβ) | d(Cβ–Cγ) | Δd(Cα–Cβ)b | Δd(Cα–Cβ)b | d(Cβ–LG)c | avg d (ring)d |
|---|---|---|---|---|---|---|
| chlorides | ||||||
| allyl | 1.501 | 1.339 | 1.780 | NA | ||
| ts | 1.464 | 1.344 | –0.037 | 0.005 | 2.340 | NA |
| propyl | 1.519 | 1.529 | 1.787 | NA | ||
| ts | 1.507 | 1.524 | –0.012 | –0.005 | 2.341 | NA |
| benzyl | 1.498 | 1.403 | 1.798 | 1.400 ± 0.002 | ||
| ts | 1.468 | 1.403 | –0.030 | 0 | 2.322 | 1.400 ± 0.003 |
| fulvenyl | 1.488 | 1.357 | 1.795 | 1.428 ± 0.050 | ||
| ts | 1.455 | 1.368 | –0.033 | 0.011 | 2.302 | 1.424 ± 0.034 |
| 5,6-dihydrofulvenyl | 1.520 | 1.536 | 1.789 | 1.439 ± 0.072 | ||
| ts | 1.510 | 1.535 | –0.010 | 0.011 | 2.319, 2.341 | 1.438 ± 0.062 |
| 6-methylfulvenyl | 1.497 | 1.365 | 1.798 | 1.428 ± 0.049 | ||
| ts | 1.464 | 1.374 | –0.033 | 0.009 | 2.291, 2.319 | 1.424 ± 0.038 |
| 6-methyl-5,6-dihydrofulvenyl | 1.525 | 1.545 | 1.792 | 1.439 ± 0.064 | ||
| ts | 1.516 | 1.547 | –0.009 | 0.002 | 2.342, 2.343 | 1.438 ± 0.063 |
| triafulvenyl | 1.484 | 1.339 | 1.816 | 1.408 ± 0.050 | ||
| ts | 1.431 | 1.342 | –0.053 | 0.003 | 2.452 | 1.406 ± 0.046 |
| 3,4-dihydrotriafulvenyl | 1.519 | 1.517 | 1.792 | 1.446 ± 0.092 | ||
| ts | 1.509 | 1.513 | –0.010 | –0.004 | 1.445 ± 0.050 | |
| acetonyle | 1.523 | 1.504 | 1.781 | NA | ||
| acetonyl tse | 1.495 | 1.508 | –0.028 | 0.004 | 2.295 | NA |
| ammonium ions | ||||||
| allyl | 1.495 | 1.342 | 1.526 | NA | ||
| ts | 1.474 | 1.345 | –0.021 | 0.003 | 2.080 | NA |
| propyl | 1.520 | 1.531 | 1.517 | NA | ||
| ts | 1.515 | 1.528 | –0.005 | –0.003 | 2.059, 2.060 | NA |
| fulvenyl | 1.502 | 1.357 | 1.523 | 1.430 ± 0.055 | ||
| ts | 1.466 | 1.360 | –0.036 | 0.003 | 2.085, 2.091 | 1.430 ± 0.053 |
| 5,6-dihydrofulvenyl | 1.521 | 1.539 | 1.517 | 1.440 ± 0.067 | ||
| ts | 1.516 | 1.530 | –0.005 | –0.009 | 2.041, 2.069 | 1.441 ± 0.066 |
| triafulvenyl | 1.350 | 1.478 | 1.547 | 1.400 ± 0.043 | ||
| ts | 1.385 | 1.385 | 0.035 | –0.093 | 2.238, 2.978 | 1.389 ± 0.025 |
| intermediate | 1.363 | 1.404 | 0.013 | –0.074 | 2.814, 2.814 | 1.384 ± 0.019 |
| 3,4-dihydrotriafulvenyl | 1.522 | 1.527 | 1.515 | 1.446 ± 0.097 | ||
| ts | 1.517 | 1.521 | –0.005 | –0.006 | 2.054, 2.061 | 1.445 ± 0.091 |
a
Calculated at the MP2/6-311+G** level.
b
Distance in transition state minus that in substrate.
c
The two C–Cl distances in the transition states are the same.
d
Average C–C distances in the phenyl ring (benzyl) or the 5-membered ring (fulvenyl/5,6-dihydrofulvenyl) or the 3-membered ring (triafulvenyl-3,4-dihydrotriafulvenyl).
e
These distances were obtained at the G3MP2 level.