Regioselectivity

In <a href="/facts/Organic_chemistry/djxhxaNg">organic chemistry</a>, regioselectivity is the preference of <a href="/facts/Chemical_bond/ArNUMnIB">chemical bonding</a> or breaking in one direction over all other possible directions. It can often apply to which of many possible positions a <a href="/facts/Reagent/c3GLInCu">reagent</a> will affect, such as which <a href="/facts/Proton/clCjepXP">proton</a> a strong <a href="/facts/Base_(chemistry)/M9wA7qeM">base</a> will <a href="/facts/Hydrogen_atom_abstraction/mqaVtjJA">abstract</a> from an <a href="/facts/Organic_compound/gqCNaN45">organic molecule</a>, or where on a substituted <a href="/facts/Benzene/Fguue7nr">benzene</a> ring a further <a href="/facts/Substituent/6y9IE6G0">substituent</a> will be added.
A specific example is a <a href="/facts/Halohydrin_formation_reaction/3j9Ih9MX">halohydrin formation reaction</a> with <a href="/facts/2-propenylbenzene/nC1gMKW8">2-propenylbenzene</a>:

Because of the preference for the formation of one <a href="/facts/Product_(chemistry)/8uCoDUdv">product</a> over another, the reaction is selective. This reaction is regioselective because it selectively generates one <a href="/facts/Constitutional_isomer/vEQEBbWQ">constitutional isomer</a> rather than the other.
Various examples of regioselectivity have been formulated as rules for certain classes of <a href="/facts/Chemical_compound/37FXqqtv">compounds</a> under certain conditions, many of which are named. Among the first introduced to chemistry students are <a href="/facts/Markovnikov%2527s_rule/WJokRx6l">Markovnikov's rule</a> for the addition of protic <a href="/facts/Acid/FySU18n1">acids</a> to <a href="/facts/Alkene/RtYcS6kU">alkenes</a>, and the <a href="/facts/F%25C3%25BCrst-Plattner_rule/pjj8YXMX">Fürst-Plattner rule</a> for the addition of <a href="/facts/Nucleophile/xYccoaJQ">nucleophiles</a> to derivatives of <a href="/facts/Cyclohexene/EWIV90Fx">cyclohexene</a>, especially <a href="/facts/Epoxide/PLxRI7r1">epoxide</a> derivatives.
Regioselectivity in <a href="/facts/Ring-closure_reaction/TH2ReKIQ">ring-closure reactions</a> is subject to <a href="/facts/Baldwin%2527s_rules/KjVB4b38">Baldwin's rules</a>. If there are two or more orientations that can be generated during a reaction, one of them is dominant (e.g., Markovnikov/anti-Markovnikov addition across a <a href="/facts/Double_bond/qDemMn0c">double bond</a>)
Regioselectivity can also be applied to specific reactions such as <a href="/facts/Addition_to_pi_ligands/1CtcRwbz">addition to pi ligands</a>.
Selectivity also occurs in <a href="/facts/Carbene/3WxNSStY">carbene</a> <a href="/facts/Insertion_reaction/Mx600UYr">insertions</a>, for example in the <a href="/facts/Baeyer-Villiger/mcrHA67l">Baeyer-Villiger</a> reaction. In this reaction, an oxygen is regioselectively inserted near an adjacent <a href="/facts/Carbonyl/KJ71bo3X">carbonyl</a> group. In <a href="/facts/Ketone/BqQXpLo4">ketones</a>, this insertion is directed toward the carbon which is more highly substituted (i.e. according to Markovnikov's rule). For example, in a study involving <a href="/facts/Acetophenone/4dk14PQz">acetophenones</a>, this oxygen was preferentially inserted between the carbonyl and the <a href="/facts/Aromatic/wK0DzRY6">aromatic</a> ring to give <a href="/facts/Acetyl/rRmtXdn3">acetyl</a> aromatic <a href="/facts/Ester/FoUAIIw4">esters</a> instead of <a href="/facts/Methyl_benzoate/x9q7J64H">methyl benzoates</a>.

Regioselectivity open-in-new

Regioselectivity