Abstract
A series of aromatic hydrocarbons were investigated so as to compare the reactivity of corannulene with planar aromatic hydrocarbons. Corannulene was found to be more reactive than benzene, naphthalene and triphenylene to Friedel-Crafts acylation whilst electrophilic aromatic bromination was also used to confirm that triphenylene was less reactive than corannulene and that pyrene, perylene and acenaphthene were more so. The stabilisation of a neighbouring carbocation by the various aromatic systems was investigated through consideration of the rates of methanolysis of a series of benzylic alcohols. The reactivity series was found to parallel that observed for the electrophilic aromatic substitutions and both series are supported by computational studies. As such, a reactivity scale was devised that showed that corannulene was less reactive than would be expected for an aromatic planar species of similar pi electron count.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) are a group of cyclic compounds consisting of fused aromatic rings that do not contain any heteroatoms; the carbon atoms are predominantly sp[2] hybridised and the pi electrons of the system delocalised.[1]
Whilst the order of reactivity towards electrophilic aromatic substitution is relatively consistent across the reactions considered, it is clear that a number of factors, including the total number of pi electrons and the potential for isolated aromatic cores[18] need to be taken into account
It is worth noting that phenanthrene 3 has been reported previously to undergo reversible Friedel–Crafts acylations to form a complex mixture of isomers,[30] which may account for the complexity of the product mixture in that case
Summary
Polycyclic aromatic hydrocarbons (PAHs) are a group of cyclic compounds consisting of fused aromatic rings that do not contain any heteroatoms; the carbon atoms are predominantly sp[2] hybridised and the pi electrons of the system delocalised.[1] First discovered in crude oils in the late 1800s,2 PAHs can either be a simple one ring extension of the monocyclic benzene 1 to give naphthalene 2 or form more complex polycycles such as phenanthrene 3, the tethered napthyl system Reactions of these species, towards electrophiles, are well studied; these reactions include the Friedel– Crafts acylation of species 1,5 2,5 3,6 5,7 78 and [8,9] and the bromination of acenaphthene 410 and pyrene 6.11 In terms of the relative reactivity of some of these species, competitive sulfonation[12] showed that reactivity increased in the order benzene 1, phenanthrene 3, naphthalene 2 and, pyrene 6 with the order of [1, 3] and 2 confirmed by Gore et al.[13] and Pryor et al.[14] Whilst no competitive bromination studies have been undertaken, a comparison of reaction conditions allows a reactivity order to be developed. Of particular interest would be the position that corannulene 8 takes in this series as complications arise as a result of the non-planarity of this species
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
