Cycloheptatriene

Structural formula
General
Surname	Cycloheptatriene
other names	Tropilids
Molecular formula	C 7 H 8
Brief description	Yellow liquid with an unpleasant odor
External identifiers / databases
CAS number 544-25-2 EC number 208-866-3 ECHA InfoCard 100.008.061 PubChem 11000 Wikidata Q421640
properties
Molar mass	92.14 g mol −1
Physical state	liquid
density	0.95 g cm −3 (25 ° C)
Melting point	−80 ° C
boiling point	117 ° C
Refractive index	1.5211
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 225-301-311-304-315-319-335 P: 210-301 + 310-303 + 361 + 353-305 + 351 + 338-361-405
Toxicological data	171 mg kg −1 ( LD 50 ,  mouse ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Cycloheptatriene (outdated: tropilides ; derived from tropane , which itself is derived from atropine ) is a cyclic unsaturated hydrocarbon with the empirical formula C ₇ H ₈ and three conjugated double bonds .

Cycloheptatriene is a structural isomer of toluene . B. can be converted photochemically .

Tropylium cation

The aromatic tropylium cation

The reaction of cycloheptatriene with bromine or hydride ion acceptors such as triphenylcarbenium tetrafluoroborate forms the aromatic tropylium cation ( cycloheptatrienylium , [C ₇ H ₇ ] ⁺ ) with elimination of a hydride ion (H ^- ):

${\displaystyle \mathrm {C_{7}H_{8}+Br_{2}\longrightarrow \ C_{7}H_{7}^{+}+Br^{-}+HBr} }$

Cycloheptatriene has an angled structure with different bond lengths between the carbon atoms , while the tropylium cation is completely planar with identical CC distances and equivalent hydrogen atoms . This cation was predicted by Hückel as early as 1931 , but was not detected until 1954 by William von Eggers Doering and Lawrence H. Knox .

Under electron impact conditions (in the mass spectrometer), almost all benzyl compounds rearrange with ring expansion before fragmentation, so that a tropylium cation is formed.

Individual evidence

1. ↑ ^{a b c d e f g} Datasheet Cycloheptatriene from AlfaAesar, accessed on January 26, 2013 ( PDF )(JavaScript required) .
2. ↑ Cycloheptatriene data sheet from Sigma-Aldrich , accessed on March 23, 2011 ( PDF ).
3. ^ JE Huheey, EA Keiter, RL Keiter: Inorganic Chemistry: Principles of Structure and Reactivity , 2003, Walter de Gruyter , ISBN 3-11-017903-2 .
4. ^ W. von E. Doering, LH Knox: The Cycloheptatrienylium (Tropylium) Ion. In: Journal of the American Chemical Society. 76, 1954, pp. 3203-3206, doi: 10.1021 / ja01641a027 .
5. ^ Collective of authors: Analytikum , VEB Deutscher Verlag für Grundstoffindustrie Leipzig, 1971, p. 338.