All other trademarks and copyrights are the property of their respective owners. Chaudhary, Ganga Ram; Karna, Shila Kant Lal; Sharma, Kanchan; Singh, Sanjay; Gupta, Dipak Kumar. Each member differs from the next by a -CH₂- group. Finar, I. L., Organic Chemistry, Vol. For each successive homologue we add CH2 to the chain. Ghosh, S.K., Advanced General Organic Chemistry, Second Edition, New Central Book Agency Pvt. For example: • Electron-dot formula : In this formula valence electrons are represented by dots placed around the chemical symbol. And we can describe the homologous series of alkynes by a general formula, CnH2n−2. 3) Due to the presence of the same functional group, all the members of a homologous series are almost similar in chemical properties. 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Alkanes : Alkanes are the saturated hydrocarbons with general formula CnH2n+2. The open chain organic compounds can be further classified as. Plus, get practice tests, quizzes, and personalized coaching to help you 1) All the members of a homologous series contain same general formula and have similar structures. © copyright 2003-2020 Study.com. Vol. So, each member of the alkane series, each homologue, contains a chain that is n lots of carbon atoms long, Cn. N, O or S ) is present as one of the ring forming atoms are called heterocyclic compounds. are composed of ONLY carbon (C) and hydrogen (H) atoms, have single covalent bonds between all the carbon atoms (C−C), have a double bond between two of the carbon atoms (C=C), have a triple bond between two of the carbon atoms (C≡C), are composed of ONLY carbon (C), hydrogen (H) and oxygen (O) atoms, have only single bonds between the carbon atoms (C−C). There are 3 double bonds i.e. A homologous series is a group of chemicals which have similar chemical properties and can be represented by a general formula. Hexane has more carbon and hydrogen atoms than pentane, so it has more London dispersion forces. Read about our approach to external linking. Earn Transferable Credit & Get your Degree, Organic Chemistry & the Study of Carbon Compound Life Forms, Alcohols & Alkanols: Classification & Functional Group, Structural Isomers: Definition & Examples, What is Pentanol? First. However, the physical properties of homologues are different because of increased London dispersion forces. An homologous series is a group of compounds with similar structural features that can be represented by a general formula whose members differ by one -CH 2 - unit. (adsbygoogle = window.adsbygoogle || []).push({}); Want chemistry games, drills, tests and more? Names and structures of the functional groups, Position isomers of propanol: 1-propanol or propan-1-ol on the left and propan-2-ol on the right. courses that prepare you to earn All the members of homologous series can be prepared by a common method of preparation. Not sure what college you want to attend yet? 14 chapters | Thus, a functional group is defined as an atom or group of atoms linked with carbon which determines characteristic properties of the organic compounds. Which of the following is a heterocyclic aromatic compound : 9. We adhere to the GDPR and EU laws and we will not share your personal information with or sell it to third-party marketers. Have you ever looked at a family photo at a friend's house and noticed how everyone kind of looked similar, but they didn't look exactly the same? Bahl, B.S., A., Advanced Organic Chemistry, S. Chand and company Ltd, New Delhi, 1992. Remember, the functional group is just the area of the molecule that is reactive or can change in chemical reactions. Try a Free Sample of our revision notes as a printable PDF. Sciences, Culinary Arts and Personal Copyright 2015 - 2020 SAVE MY EXAMS! The alkane homologous series contains compounds that: Since one carbon will make a total of 4 covalent bonds, the first member (homologue) of the alkane homologous series must be 1 carbon atom bonded to 4 hydrogen atoms as shown below: The next homologue in the alkane homologous series will contain 2 carbon atoms with a single covalent bond between them, each carbon atom will make up its quota of 4 covalent bonds by bonding to 3 hydrogen atoms as shown below: and this molecule has the molecular formula C2H6. Select a subject to preview related courses: For example, the boiling point of pentane is 36.1o C, while the boiling point of the homologue hexane is 68.7o C. What causes that 30 degree jump in boiling point? Homologous series The series of organic compounds having same general formula and similar chemical properties but different physical properties in which one member differs from other member by single – CH 2 unit is known as homologous series. just create an account. Alkenes are also called olefins ( i.e. Benzene is cyclic and planar and has cyclic overlap of p-orbitals. 10 ORGANIC CHEMISTRY HOMOLOGOUS SERIES The alkanes form a series of compounds all with the general formula C n H 2n+2, e.g. For example: 2. Both are alkanes (all C and H atoms connected with single bonds). The increase in boiling point is due to increased London dispersion forces, or attractions between the molecules. Hydrocarbons are compounds that contain only hydrogen and carbon. Alkanal homologous series contains compounds that: The first member (homologue) of the alkanal homologous series contains only 1 carbon atom, which must make 4 bonds in total and 2 of those bonds are to an oxygen atom, as shown below: The second member (homologue) of the alkanal homologous series contains 2 carbon atoms, each of which must make 4 bonds in total, and the end carbon atom must make 2 bonds to an oxygen atom, as shown below: The third member (homologue) of the alkanal homologous series contains 3 carbon atoms, each of which must make 4 bonds in total, and the end carbon atom must make 2 bonds to an oxygen atom, as shown below: The general formula for members of the alkanal homologous series is CnH2nO, The first member of the alkanal homologous series has n=1, so the molecular formula of the first homologue is C1H2×1O, that is, CH2O, The second member of the alkanal homologous series has n=2, so the molecular formula of the second homologue is C2H2×2O, that is, C2H4O. The first homologous series is the alkanes. For example: Each member of homologous series is called homologue and phenomenon of making homologous series is called homology. b. This can be the length of a carbon chain, for example in the straight-chained alkanes (paraffins), or it could be the number of monomers in a homopolymer such as amylose. Putting it all together allows us to write a general formula for the homologous series of alkanes: CnH2n+2, For the first member of the alkane series (the first homologue), n=1 so the molecular formula will be C1H2×1+2 which is CH4, For the second member of the alkane series (the second homologue), n=2 so the molecular formula will be C2H2×2+2 which is C2H6. Community smaller than society. Recent developments in chemistry written in language suitable for students. 5) There is a regular gradation in the physical properties like melting point, density etc. imaginable degree, area of The formula of methane is CH4 and the formula of ethane is C2 H6. Anyone can earn (ii) differ by a constant unit as you proceed from one member to another. c. Butane, 2-methylpropane, 2-methylbutane, d. Chloroathane, 2-chloropropane, 1-chlorobutane. Occupation, Business & Technology Education, Fundamental Principles of Organic Chemistry, Empirical, Molecular Formula And Limiting Reagents, Introduction to Atomic Mass and Molecular Mass, Avogadro's Hypothesis and Its Application, Introduction to Avogadro's Hypothesis and its Applications, Introduction to Periodic Classification of Elements, Introduction,structure and preparation of Ozone, Introduction to Boron, Silicon and periodic Position, Water Pollution and Greenhouse Effects(Global warming), Preliminary ideas about reaction and Fundamental principles, Nomenclature of Compounds Containing Single Functional Group, Vital Force Theory, Its Limitations, And Definition of Organic Chemistry, Qualitative Analysis of Organic Compounds, Nomenclature of Compounds Containing Polyfunctional Group, Introduction of organic chemistry, classification of organic compounds, Organic Reactions and Preliminary Concept of Reaction Mechanism, Electronic Effects Affecting a Covalent Bond, Organic compound consists of two parts, a reactive (active) part, which is known as a functional group and a skeletal part consisting of carbon and hydrogen atoms, which is known as the alkyl group (Its general formula is C. A functional group is defined as an atom or group of atoms linked with carbon which determines characteristic properties of the organic compounds.