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Homologous series
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<h2 id="examples">Examples</h2> <p>The homologous series of straight-chained alkanes begins <a href="/facts/Methane/kBHneYnh">methane</a> (CH4), <a href="/facts/Ethane/BGCzc6yh">ethane</a> (C2H6), <a href="/facts/Propane/E0b23KGh">propane</a> (C3H8), <a href="/facts/Butane/InIHpYlY">butane</a> (C4H10), and <a href="/facts/Pentane/B5LzJ2zD">pentane</a> (C5H12). In that series, successive members differ in mass by an extra <a href="/facts/Methylene_bridge/t3lvUJuT">methylene bridge</a> (-CH2- unit) inserted in the chain. Thus the <a href="/facts/Molecular_mass/FWueGMed">molecular mass</a> of each member differs by 14 <a href="/facts/Atomic_mass/J1FJY9MV">atomic mass</a> units. Adjacent members in such a series, such as methane and ethane, are known as "adjacent homologues".<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> <p>Within that series, many physical properties such as <a href="/facts/Boiling_point/E2BK9QoS">boiling point</a> gradually change with increasing mass. For example, ethane (C2H6), has a higher boiling point than methane (CH4). This is because the <a href="/facts/London_dispersion_force/zU842d26">London dispersion forces</a> between ethane molecules are higher than that between methane molecules, resulting in stronger forces of intermolecular attraction, raising the boiling point. </p> <p>Some important classes of organic molecules are <a href="/facts/Derivative_(chemistry)/JYcbLkbm">derivatives</a> of alkanes, such as the primary <a href="/facts/Alcohol_(chemistry)/Y0SCTDkh">alcohols</a>, <a href="/facts/Aldehyde/xSIRkW03">aldehydes</a>, and (mono)<a href="/facts/Carboxylic_acid/U4xuMosy">carboxylic acids</a> form analogous series to the alkanes. The corresponding homologous series of primary straight-chained <a href="/facts/Alcohol_(chemistry)/Y0SCTDkh">alcohols</a> comprises <a href="/facts/Methanol/EIfpoNCg">methanol</a> (CH4O), <a href="/facts/Ethanol/3lCLfBSP">ethanol</a> (C2H6O), <a href="/facts/1-propanol/NoSmhEhh">1-propanol</a> (C3H8O), <a href="/facts/1-butanol/GlSNHexW">1-butanol</a>, and so on. The single-ring <a href="/facts/Cycloalkane/8dQAoD1N">cycloalkanes</a> form another such series, starting with <a href="/facts/Cyclopropane/BAUAYB7s">cyclopropane</a>. </p> <table><tbody><tr><td>Homologous series</td><td>General formula</td><td>Repeating unit</td><td>Functional group(s)</td></tr><tr><td>Straight-chain <a href="/facts/Alkane/Qam7Hvmf">alkanes</a></td><td>C<i>n</i>H2<i>n</i> + 2 (<i>n</i> ≥ 1)</td><td><a href="/facts/Methylene_bridge/t3lvUJuT">−CH2−</a></td><td><a href="/facts/Methyl_group/fkM97EMD">H3C−</a> ... −CH3</td></tr><tr><td>Straight-chain <a href="/facts/Perfluoroalkane/jA9N6aoT">perfluoroalkanes</a></td><td>C<i>n</i>F2<i>n</i> + 2 (<i>n</i> ≥ 1)</td><td>−CF2−</td><td><a href="/facts/Trifluoromethyl/cMG8jjRN">F3C−</a> ... −CF3</td></tr><tr><td>Straight-chain <a href="/facts/Alkyl/vmEk8X4v">alkyl</a></td><td>C<i>n</i>H2<i>n</i> + 1 (<i>n</i> ≥ 1)</td><td>−CH2−</td><td>H3C− ... −CH2−</td></tr><tr><td>Straight-chain <a href="/facts/1-alkene/lzbLgU7Q">1-alkenes</a></td><td>C<i>n</i>H2<i>n</i> (<i>n</i> ≥ 2)</td><td>−CH2−</td><td><a href="/facts/Methylene_group/sdGv7zMu">H2C=</a>CH− ... −CH3</td></tr><tr><td><a href="/facts/Cycloalkane/8dQAoD1N">Cycloalkanes</a></td><td>C<i>n</i>H2<i>n</i> (<i>n</i> ≥ 3)</td><td>−CH2−</td><td>Singly-bonded ring</td></tr><tr><td>Straight-chain 1-<a href="/facts/Alkyne/VHI4N5Wo">alkynes</a></td><td>C<i>n</i>H2<i>n</i> − 2 (<i>n</i> ≥ 2)</td><td>−CH2−</td><td><a href="/facts/Methylidyne_group/VR8mq7YS">HC≡</a>C− ... −CH3</td></tr><tr><td><a href="/facts/Polyacetylene/0Adw1YQY">Polyacetylenes</a></td><td>C2<i>n</i>H2<i>n</i> + 2 (<i>n</i> ≥ 2)</td><td><a href="/facts/Vinylene_group/KgllEpYS">−CH=CH−</a></td><td>H3C− ... −CH3</td></tr><tr><td>Straight-chain primary <a href="/facts/Alcohol_(chemistry)/Y0SCTDkh">alcohols</a></td><td>C<i>n</i>H2<i>n</i> + 1OH (<i>n</i> ≥ 1)</td><td>−CH2−</td><td>H3C− ... −OH</td></tr><tr><td>Straight-chain primary mono<a href="/facts/Carboxylic_acid/U4xuMosy">carboxylic acids</a></td><td>C<i>n</i>H2<i>n</i> + 1COOH (<i>n</i> ≥ 0)</td><td>−CH2−</td><td>H3C− ... −COOH</td></tr><tr><td><a href="/facts/Polyethylene_glycol/tC7xBFwr">Polyethylene glycol</a> oligomers</td><td>C2nH4n+2On+1 (<i>n</i> ≥ 2)</td><td>−(O−CH2−CH2)−</td><td>HO−CH2−CH2− ... −OH</td></tr><tr><td>Straight-chain <a href="/facts/Azane/hRSo5EbY">azanes</a></td><td>N<i>n</i>H<i>n</i> + 2 (<i>n</i> ≥ 1)</td><td>−NH−</td><td>H2N− ... −NH2</td></tr></tbody></table> <p><a href="/facts/Biopolymers/GaCwr4EY">Biopolymers</a> also form homologous series, for example the polymers of <a href="/facts/Glucose/oUSkoLCD">glucose</a> such as <a href="/facts/Cellulose/wYPafTU0">cellulose</a> oligomers<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> starting with <a href="/facts/Cellobiose/NobrXY99">cellobiose</a>, or the series of <a href="/facts/Amylose/FJBcmQ2v">amylose</a> oligomers starting with <a href="/facts/Maltose/v43CVtaU">maltose</a>, which are sometimes called maltooligomers.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> Homooligopeptides, <a href="/facts/Oligopeptide/rM2AHGNV">oligopeptides</a> made up of repetitions of only one amino acid can also be studied as homologous series.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p> <h2 id="inorganic-homologous-series">Inorganic homologous series</h2> Wikimedia Commons has media related to Homologous series. <p>Homologous series are not unique to <a href="/facts/Organic_chemistry/djxhxaNg">organic chemistry</a>. <a href="/facts/Titanium/53ArnDoy">Titanium</a>, <a href="/facts/Vanadium/UvKkKTSm">vanadium</a>, and <a href="/facts/Molybdenum/RX6vp2bF">molybdenum</a> <a href="/facts/Oxides/DXtoVe1C">oxides</a> all form homologous series (e.g. V<i>n</i>O2<i>n</i> − 1 for 2 < <i>n</i> < 10), called Magnéli phases,<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> as do the <a href="/facts/Silanes/1t4s6Icu">silanes</a>, Si<i>n</i>H2<i>n</i> + 2 (with <i>n</i> up to 8) that are analogous to the alkanes, C<i>n</i>H2<i>n</i> + 2. </p> <h2 id="periodic-table">Periodic table</h2> <p>On the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a>, homologous elements share many <a href="/facts/Electrochemical_reaction_mechanism/KI0jQqVC">electrochemical</a> properties and appear in the same <a href="/facts/Group_(periodic_table)/YGBcUabv">group</a> (column) of the table. For example, all <a href="/facts/Noble_gases/j0yHMEAE">noble gases</a> are colorless, <a href="/facts/Monatomic_gas/1cTX2U2g">monatomic gases</a> with very low reactivity. These similarities are due to similar structure in their <a href="/facts/Electron_shell/QxI30eh9">outer shells</a> of <a href="/facts/Valence_electrons/mXPA15VP">valence electrons</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> <a href="/facts/Dmitri_Mendeleev/xdouRrx8">Mendeleev</a> used the prefix <a href="/facts/Eka-/C4vgW0uy">eka-</a> for an unknown element below a known one in the same group. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Analog_(chemistry)/3aysWSVG">Analog</a></li> <li><a href="/facts/Congener_(chemistry)/8qy2rvGG">Congener</a></li> <li><a href="/facts/Ruddlesden-Popper_phase/t8ETAC2t">Ruddlesden-Popper phase</a></li> <li><a href="/facts/Structure%25E2%2580%2593activity_relationship/S2RxpCUK">Structure–activity relationship</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Glossary of Terms Used in Medicinal Chemistry (IUPAC Recommendations 1998)". Archived from the original on 2017-08-25. Retrieved 2007-12-22. <a href="https://web.archive.org/web/20170825024257/http://www.chem.qmul.ac.uk/iupac/medchem/ah.html#h5" target="_blank">https://web.archive.org/web/20170825024257/http://www.chem.qmul.ac.uk/iupac/medchem/ah.html#h5</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Brown, Theodore L. (Theodore Lawrence); LeMay, H. Eugene (Harold Eugene); Bursten, Bruce Edward (1991). Chemistry: the central science (5th ed.). Englewood Cliffs, NJ: Prentice Hall. pp. 940. ISBN 978-0-13-126202-7. OCLC 21973767. <a href="978-0-13-126202-7" target="_blank">978-0-13-126202-7</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Brown, Theodore L. (Theodore Lawrence); LeMay, H. Eugene (Harold Eugene); Bursten, Bruce Edward (1991). Chemistry: the central science (5th ed.). Englewood Cliffs, NJ: Prentice Hall. pp. 940. ISBN 978-0-13-126202-7. OCLC 21973767. <a href="978-0-13-126202-7" target="_blank">978-0-13-126202-7</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Saarela, K. (2013-10-22). Macromolecular Chemistry—8: Plenary and Main Lectures Presented at the International Symposium on Macromolecules Held in Helsinki, Finland, 2–7 July 1972. Elsevier. p. 88. ISBN 978-1-4832-8025-7. <a href="978-1-4832-8025-7" target="_blank">978-1-4832-8025-7</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Glossary of Terms Used in Medicinal Chemistry (IUPAC Recommendations 1998)". Archived from the original on 2017-08-25. Retrieved 2007-12-22. <a href="https://web.archive.org/web/20170825024257/http://www.chem.qmul.ac.uk/iupac/medchem/ah.html#h5" target="_blank">https://web.archive.org/web/20170825024257/http://www.chem.qmul.ac.uk/iupac/medchem/ah.html#h5</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Charles Gerhardt (1843) "Sur la classification chimique des substances organiques" (On the chemical classification of organic substances), Revue scientifique et industrielle, 14 : 580–609. From page 588: "17. Nous appelons substances homologues celles qui jouissent des même propriétés chimiques et dont la composition offre certaines analogies dans les proportions relatives des éléments." (17. We call homologous substances those that have the same chemical properties and whose composition offers certain analogies in the relative proportion of elements.) <a href="https://books.google.com/books?id=CfqOt7jLYrAC&pg=PA580" target="_blank">https://books.google.com/books?id=CfqOt7jLYrAC&pg=PA580</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>See In re Henze, 181 F.2d 196, 201 (CCPA 1950), in which the court stated, "In effect, the nature of homologues and the close relationship the physical and chemical properties of one member of a series bears to adjacent members is such that a presumption of unpatentability arises against a claim directed to a composition of matter, the adjacent homologue of which is old in the art." <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Rojas, Orlando J. (2016-02-25). Cellulose Chemistry and Properties: Fibers, Nanocelluloses and Advanced Materials. Springer. ISBN 978-3-319-26015-0. <a href="978-3-319-26015-0" target="_blank">978-3-319-26015-0</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Advances in Carbohydrate Chemistry and Biochemistry. Academic Press. 1981-06-19. ISBN 978-0-08-056297-1. <a href="978-0-08-056297-1" target="_blank">978-0-08-056297-1</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Giddings, J. Calvin (1982-08-25). Advances in Chromatography. CRC Press. ISBN 978-0-8247-1868-8. <a href="978-0-8247-1868-8" target="_blank">978-0-8247-1868-8</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Schwingenschlögl, U.; Eyert, V. (2004-09-01). "The vanadium Magnéli phases VnO2n-1". Annalen der Physik. 13 (9): 475–510. arXiv:cond-mat/0403689. doi:10.1002/andp.200410099. ISSN 0003-3804. S2CID 116832557. <a href="https://onlinelibrary.wiley.com/doi/10.1002/andp.200410099" target="_blank">https://onlinelibrary.wiley.com/doi/10.1002/andp.200410099</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Guillermet, A. Fernández; Grimvall, G. (15 July 1989). "Homology of interatomic forces and Debye temperatures in transition metals". Physical Review B. 40 (3): 1521–1527. Bibcode:1989PhRvB..40.1521G. doi:10.1103/PhysRevB.40.1521. PMID 9992004. <a href="https://www.researchgate.net/publication/13297475" target="_blank">https://www.researchgate.net/publication/13297475</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> </ol>