ORGANIC NAMING - Lecture Notes

ORGANIC CHEMISTRY SOME BASIC PRINCIPLES AND TECHNIQUES PART 1 NOMENCLATURE The word organic signifies life - ie, compounds directly or indirectly derived from living beings. Lemery classified the naturally occurring substances into 3 1. Mineral substances 2. Vegetable substances 3. Animal substances Lavoisier reclassified theses in to two based on a some elements common in vegetable and animal substances 1. Compounds from living beings ( Organic compounds) 2. Compounds form non living beings ( Inorganic compounds) Organic Chemistry- The branch of chemistry deals with study about organic compounds. Berzelius - Vital force theory Organic compounds are produced only under the influence of some mysterious force existing in living beings, such a force cannot be created artificially in laboratories. In 1828 - Wohler discovered urea by heating an inorganic compound. Later Kolbe synthesis acetic acid Berthelot synthesised methane and acetylene Thus vital force theory was rejected and it was shown that organic compounds should be synthesised from inorganic source. Organic Chemistry- Is the study about carbon and its compounds or Hydrocarbon and their derivatives. BONDING IN CARBON - THE COVALENT BOND The reactivity of elements is explained as their tendency to attain a completely filled outer shell, that is, attain noble gas configuration. Elements forming ionic compounds achieve this by either gaining or losing electrons from the outermost shell. In the case of carbon, it has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration. There are two possibilities (i) It could gain four electrons forming C4- anion, but it would be difficult for the nucleus with six protons to hold onto ten electrons, i.e., four extra electrons. (ii) It could lose four electrons forming C4+ cation, but it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding onto just two electrons. Carbon overcomes the problem by sharing its valence electrons with other carbon atoms or atoms of other elements. The shared electrons belong to the outer shell of both the atoms and lead to both atoms attaining noble gas configuration.

VERSATILE NATURE OF CARBON (i) Catenation : The property of self-linking of atoms through covalent bonds to form long straight and branched chains and rings of different sizes is called catenation. Carbon shows maximum catenation due to small size, electronic configuration and unique strength of carbon - carbon bonds. (ii) Tetravalency of carbon : Carbon belongs to group 14 of the periodic table. It has four electrons in its outermost shell and therefore, its valency is four. Carbon forms four covalent bonds in its compouds. A methane molecule (CH4) is formed when four electrons of a carbon atom are shared with four hydrogen atoms: (iii) Tendency to form multiple bonds : Due to small size, carbon can form multiple bonds (double and triple bonds) by sharing more than one electron pair. As a result, it can form a variety of compounds. TETRAVALENCE OF CARBON: SHAPES OF ORGANIC COMPOUNDS Hybridisation influences the bond length and bond enthalpy (strength) in organic compounds. The sp hybrid orbital contains more s character and hence it is closer to its nucleus and forms shorter and stronger bonds than the sp3 hybrid orbital. The sp2 hybrid orbital is intermediate in s character between sp and sp3 and, hence, the length and enthalpy of the bonds it forms, are also intermediate between them. The change in hybridisation affects the electronegativity of carbon. The greater the s character of the hybrid orbitals, the greater is the electronegativity. Thus, a carbon atom having an sp hybrid orbital with 50% s character is more electronegative than that possessing sp2 or sp3 hybridised orbitals. SP3 hybridisation occurs when a C has 4 attached groups, it has 25%S and 75% P character, each SP3 hybrid orbital is in sigma bond formation. STRUCTURAL REPRESENTATIONS OF ORGANIC COMPOUNDS Complete, Condensed and Bond-line Structural Formulas Complete structural formulas. The Lewis dot structure is considered as the complete structural formula. In Lewis structure, the covalent bonds in the compound are denoted by a dash (―). This helps to emphasize the number of bonds formed by the electrons. Every single bond, a double bond, and a triple bond are represented by one dash, double dash, and triple dash respectively. It illustrates every single bond formed between every atom in the compound, thus called complete structural formula.

Condensed Structural Formula This is the condensed structural formula, where replacing some dashes/bonds by a number of identical groups attached to an atom by a subscript. Bond Line Structural Formula Here, every bond is represented as a line in a zigzag manner. If not specified, every terminal is assumed to be a methyl (-CH3) group. 3-D Representation of Organic Compounds In these formulas the solid-wedge is used to indicate a bond projecting out of the plane of paper, towards the observer. The dashed-wedge is used to depict the bond projecting out of the plane of the paper and away from the observer. Wedges are shown in such a way that the broad end of the wedge is towards the observer. The bonds lying in plane of the paper are depicted by using a normal line (—).



Nomenclature 2 system of naming 1. TRIVIAL system 2. IUPAC system



ii) ALKENE The common names of Alkenes are obtained by replacing ane in alkane by ylene CH, -_CHz Ethylene City - cH=cHz Propylene 91-13 lsobatgleneCH} - c=cHz iii) ALKYNES First member of alkyne series is ACETYLENE and others are derivatives of acetylene cH=cH Acetylene CH, -CECH Methyl acetylene CH} c- :c - city Dimethyl acetylene cars - c=c- CHIH} Ethyl methyl acetylene



















Seniority table