Search results
Results from the WOW.Com Content Network
For nitration, for example, fluorine directs strongly to the para position because the ortho position is inductively deactivated (86% para, 13% ortho, 0.6% meta). On the other hand, iodine directs to ortho and para positions comparably (54% para and 45% ortho, 1.3% meta). [12]
Groups with unshared pairs of electrons, such as the amino group of aniline, are strongly activating (some time deactivating also in case of halides) and ortho/para-directing by resonance. Such activating groups donate those unshared electrons to the pi system, creating a negative charge on the ortho and para positions. These positions are thus ...
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.
Ortho-, meta-and para-positions of a phenyl group, with respect to a substituent group "G". Made with the free software program ChemTool , and fine-tuned editing by hand with Vim (text editor) . Source
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.
For meta-directing groups (electron withdrawing group or EWG), σ meta and σ para are more positive than σ’. (The superscript, c, in table denotes data from Hammett, 1940. [11] [page needed]) For ortho-para directing groups (electron donating group or EDG), σ’ more positive than σ meta and σ para.
In organic chemistry, a directing group (DG) is a substituent on a molecule or ion that facilitates reactions by interacting with a reagent.The term is usually applied to C–H activation of hydrocarbons, where it is defined as a "coordinating moiety (an 'internal ligand'), which directs a metal catalyst into the proximity of a certain C–H bond."
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 ...