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The prefixes ortho, meta, and para are all derived from Greek, meaning correct, following, and beside, respectively. The relationship to the current meaning is perhaps not obvious. The ortho description was historically used to designate the original compound, and an isomer was often called the meta compound.
The ortho effect also occurs when a meta-directing group is positioned in a meta arrangement relative to an ortho–para-directing group, a new substituent introduced into the molecule tends to preferentially occupy the ortho position relative to the meta-directing group rather than the para position.
There are 2 ortho positions, 2 meta positions and 1 para position on benzene when a group is attached to it. When a group is an ortho / para director with ortho and para positions reacting with the same partial rate factor, we would expect twice as much ortho product as para product due to this statistical effect.
These positions are thus the most reactive towards an electron-poor electrophile. This increased reactivity might be offset by steric hindrance between activating group and electrophile but on the other hand there are two ortho positions for reaction but only one para position. Hence the final outcome of the electrophilic aromatic substitution ...
[11] [page needed]) For ortho-para directing groups (electron donating group or EDG), σ’ more positive than σ meta and σ para. The difference between σ para and σ’ (σ para – σ’) is greater than that between σ meta and σ’(σ meta − σ’). This is expected as electron resonance effects are felt more strongly at the p-positions.
Positions on an aromatic ring relative to the R group. In chemistry, meta is a prefix, used for systematic names in IUPAC nomenclature. It has several meanings. [1] In organic chemistry, meta indicates the positions of substituents in aromatic cyclic compounds. The substituents have the 1,3-positions, for example in resorcinol.
Structures of the three isomers of tolyl group. In organic chemistry, tolyl groups are functional groups related to toluene. [1] They have the general formula CH 3 C 6 H 4 −R, the change of the relative position of the methyl and the R substituent on the aromatic ring can generate three possible structural isomers 1,2 (ortho), 1,3 (meta), and 1,4 (para).
Directed ortho metalation (DoM) is an adaptation of electrophilic aromatic substitution in which electrophiles attach themselves exclusively to the ortho-position of a direct metalation group or DMG through the intermediary of an aryllithium compound. [1] The DMG interacts with lithium through a hetero atom.