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IR-Spectroscopic and X-ray-Structural Study of Vinyl-Type Carbocations in Their Carborane Salts
Evgenii S Stoyanov1, Irina Yu Bagryanskaya1, Irina V Stoyanova1
1N.N. Vorozhtsov Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences, Novosibirsk 630090, Russia.
ACS Omega
|August 15, 2022
Summary
The structure of butylene carbocations is significantly influenced by their anionic environment. Spectroscopic analysis reveals how anion ordering affects charge distribution and C=C bond frequencies in these important chemical intermediates.
Area of Science:
- Carbocation chemistry
- Spectroscopy
- Crystallography
Background:
- Carbocations are key intermediates in organic chemistry.
- The influence of counterions on carbocation structure is crucial.
- Understanding these interactions aids in predicting reactivity.
Purpose of the Study:
- To characterize butylene carbocation isomers using IR spectroscopy and X-ray diffraction.
- To investigate the impact of anionic environment on carbocation structure and bonding.
- To elucidate the electronic effects of substituents on carbocation stability.
Main Methods:
- Infrared (IR) spectroscopy to analyze vibrational frequencies.
- X-ray diffraction analysis to determine solid-state structures.
- Synthesis and characterization of butylene carbocation salts.
Main Results:
- Cation structure is dictated by the geometric ordering of the anion.
- In crystalline phases, a central -CH=C+- moiety is observed with a νC=C of 1490 cm⁻¹.
- Amorphous phases show terminal C=C bonds in contact ion pairs, with higher νC=C.
- Chlorine substitution and bulky silyl/t-Bu groups significantly alter C=C bond character and frequency.
Conclusions:
- The anionic environment plays a dominant role in stabilizing butylene carbocations.
- Electronic effects of substituents can dramatically influence the C=C bond character, sometimes exceeding neutral alkene frequencies.
- This study provides fundamental insights into the structure-property relationships of carbocations.
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