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Axial chirality
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<h2 id="nomenclature">Nomenclature</h2> <p>The <a href="/facts/Enantiomer/wjPv5J3y">enantiomers</a> of axially chiral compounds are usually given the stereochemical labels (<i>R</i>a) and (<i>S</i>a),<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> sometimes abbreviated (<i>R</i>) and (<i>S</i>).<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> The designations are based on the same <a href="/facts/Cahn%E2%80%93Ingold%E2%80%93Prelog_priority_rules/nkVS9xAq">Cahn–Ingold–Prelog priority rules</a> used for tetrahedral stereocenters.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> The chiral axis is viewed end-on and the two "near" and two "far" substituents on the axial unit are ranked, but with the additional rule that the two near substituents have higher priority than the far ones.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <i>R</i> and <i>S</i> configurations are determined by precedences of the groups attached to the axial section of the molecule when viewed along that axis. <h2 id="helical-chirality">Helical chirality</h2> <p>The chirality of a molecule that has a helical, propeller, or screw-shaped geometry is called <i>helicity</i><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> or <i>helical chirality</i>.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a><a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> The <a href="/facts/Screw_axis/Cos1gnJb">screw axis</a> or the <i>D</i><i>n</i>, or <i>C</i><i>n</i> principle <a href="/facts/Molecular_symmetry/BrDxAkTK">symmetry axis</a> is considered to be the axis of chirality. Some sources consider helical chirality to be a type of axial chirality,<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> and some do not.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a><a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> <a href="/facts/IUPAC/2AV6myCK">IUPAC</a> does not refer to helicity as a type of axial chirality.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a><a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p><p>Enantiomers having helicity may labeled by using the prefix notation (<i>P</i>) ("plus") or Δ (from Latin <i>dexter</i>, "right") for a right-handed helix, and (<i>M</i>) ("minus") or Λ (Latin <i>levo</i>, "left") for a left-handed helix.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a><a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a><a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> The <i>P</i>/<i>M</i> or Δ/Λ terminology is used particularly for molecules that actually resemble a helix, such as the <a href="/facts/Helicenes/nVAUgdzq">helicenes</a>. This notation can also be applied to non-helical structures having axial chirality by considering the helical orientation of the Cahn–Ingold–Prelog group rankings of the "front" groups compared to the "back", when viewed from either direction along the axis. </p> <i>P</i> helicity<i>M</i> helicityConfigurations of [7]<a href="/facts/Helicene/nVAUgdzq">helicene</a> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20050123014310/http://siggy.chem.ucla.edu/VOH/30A/Dinitrobiphenyl_%28COOH%292.pdf#search='axial%20chirality'">Axial Chirality in 6,6′-Dinitrobiphenyl-2,2′-dicarboxylic acid 3D representation</a>.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "axial chirality". doi:10.1351/goldbook.A00547 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Eliel, Ernest L.; Wilen, Samuel H.; Mander, Lewis N. (1994). Stereochemistry of organic compounds. New York: Wiley. ISBN 0-471-01670-5. OCLC 27642721. <a href="0-471-01670-5" target="_blank">0-471-01670-5</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "axial chirality". doi:10.1351/goldbook.A00547 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Cross, L. C.; Klyne, W. (1976). "Rules for the Nomenclature of Organic Chemistry. Section E: Stereochemistry (Recommendations 1974)". Pure Appl. Chem. 45 (1): 11–30. doi:10.1351/pac197645010011. ISSN 1365-3075. <a href="http://publications.iupac.org/pac/45/1/0011/index.html" target="_blank">http://publications.iupac.org/pac/45/1/0011/index.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Cross, L. C.; Klyne, W. (1976). "Rules for the Nomenclature of Organic Chemistry. Section E: Stereochemistry (Recommendations 1974)". Pure Appl. Chem. 45 (1): 11–30. doi:10.1351/pac197645010011. ISSN 1365-3075. <a href="http://publications.iupac.org/pac/45/1/0011/index.html" target="_blank">http://publications.iupac.org/pac/45/1/0011/index.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Cross, L. C.; Klyne, W. (1976). "Rules for the Nomenclature of Organic Chemistry. Section E: Stereochemistry (Recommendations 1974)" (PDF). Pure Appl. Chem. 45: 11–30. doi:10.1351/pac197645010011. Chiral axis. The structure is regarded as an elongated tetrahedron and viewed along the axis—it is immaterial from which end it is viewed; the nearer pair of ligands receives the first two positions in the order of preference <a href="http://publications.iupac.org/pac/1976/pdf/4501x0011.pdf" target="_blank">http://publications.iupac.org/pac/1976/pdf/4501x0011.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "helicity". doi:10.1351/goldbook.H02763 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Tan, Bin (2021). Axially Chiral Compounds: Asymmetric Synthesis and Applications. ISBN 978-3-527-82517-2. OCLC 1264474520. <a href="978-3-527-82517-2" target="_blank">978-3-527-82517-2</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Clark, Andrew; Kitson, Russell R. A.; Mistry, Nimesh; Taylor, Paul; Taylor, Matthew; Lloyd, Michael; Akamune, Caroline (2021). Introduction to Stereochemistry. ISBN 978-1-78801-315-4. OCLC 1180250839. <a href="978-1-78801-315-4" target="_blank">978-1-78801-315-4</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Clark, Andrew; Kitson, Russell R. A.; Mistry, Nimesh; Taylor, Paul; Taylor, Matthew; Lloyd, Michael; Akamune, Caroline (2021). Introduction to Stereochemistry. ISBN 978-1-78801-315-4. OCLC 1180250839. <a href="978-1-78801-315-4" target="_blank">978-1-78801-315-4</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Tan, Bin (2021). Axially Chiral Compounds: Asymmetric Synthesis and Applications. ISBN 978-3-527-82517-2. OCLC 1264474520. <a href="978-3-527-82517-2" target="_blank">978-3-527-82517-2</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Zhang, Dawei; Mulatier, Jean-Christophe; Cochrane; et al. (2016-05-02). "Helical, Axial, and Central Chirality Combined in a Single Cage: Synthesis, Absolute Configuration, and Recognition Properties". Chemistry - A European Journal. 22 (24): 8038–8042. doi:10.1002/chem.201600664. ISSN 0947-6539. PMID 27037555. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "helicity". doi:10.1351/goldbook.H02763 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "axial chirality". doi:10.1351/goldbook.A00547 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "helicity". doi:10.1351/goldbook.H02763 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Cross, L. C.; Klyne, W. (1976). "Rules for the Nomenclature of Organic Chemistry. Section E: Stereochemistry (Recommendations 1974)". Pure Appl. Chem. 45 (1): 11–30. doi:10.1351/pac197645010011. ISSN 1365-3075. <a href="http://publications.iupac.org/pac/45/1/0011/index.html" target="_blank">http://publications.iupac.org/pac/45/1/0011/index.html</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>"VLU: Additional Chirality Elements - Chemgapedia". Archived from the original on 2011-07-18. Retrieved 2007-08-06. <a href="https://web.archive.org/web/20110718212715/http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/stereochemie/weitere_chiralitaetselem.vlu/Page/vsc/en/ch/12/oc/stereochemie/helicale_chiralitaet/helicale_chiralitaet.vscml.html" target="_blank">https://web.archive.org/web/20110718212715/http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/stereochemie/weitere_chiralitaetselem.vlu/Page/vsc/en/ch/12/oc/stereochemie/helicale_chiralitaet/helicale_chiralitaet.vscml.html</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> </ol>