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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.
Since "normal" room-temperature hydrogen is a 3:1 ortho:para mixture, its molar residual rotational energy at low temperature is (3/4) × 2Rθ rot ≈ 1091 J/mol, [citation needed] which is somewhat larger than the enthalpy of vaporization of normal hydrogen, 904 J/mol at the boiling point, T b ≈ 20.369 K. [10] Notably, the boiling points of ...
Diagram showing the ortho, meta and para positions relative to a substituent X on a benzene ring. Both the regioselectivity—the diverse arene substitution patterns—and the speed of an electrophilic aromatic substitution are affected by the substituents already attached to the benzene ring.
Directed metallation is not limited to lithium intermediates or even to an ortho preference. In one study [13] it is found that the reaction product of N,N-dimethylaniline with a complex of TMEDA, sodium salt of TMP and di-tert-butylzinc is a meta zincated complex as a stable crystalline compound.
These are usually two independent single substituents, but in case of fused ring systems, ortho-fusing is also mentioned unless the substitution pattern is regarded in the name like in [2.2]paracyclophane. In the current systematic nomenclature, o-, m- and p- are often replaced by using locants (1,2-dimethylbenzene instead of o-xylene).
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).
The meta and para have the greater commercial significance. All are colorless liquids. [1] Nomenclature. Ortho: known as 1,2-diethylbenzene and o ...