Alkenes, Cycloalkenes and Alkynes PDF

Alkene, Cycloalkenes and Alkyne  Alkenes - HC that contains one or more double bonds - Sometimes called OLEFINS “oil-forming gas” - Non polar - General Formula (CnH2n) Properties of Alkenes - Unsaturated HC - Boiling points are slightly less than the boiling points of si...

Alkene, Cycloalkenes and Alkyne  Alkenes - HC that contains one or more double bonds - Sometimes called OLEFINS “oil-forming gas” - Non polar - General Formula (CnH2n) Properties of Alkenes - Unsaturated HC - Boiling points are slightly less than the boiling points of similar sized alkanes - Non- polar – low solubility in water - More reactive than alkanes Cis– Trans ( Geometric ) Isomers Naming Alkenes Rule 1: The chain chosen as the parent chain must contain the carbon-carbon double bond ( C= C) Rule 2: The parent chain must be numbered to give the carbon-carbon double bond the lowest possible number. Rule 3: The name of alkene must contain a number to indicate the position of the double Example of Alkenes Cycloalkenes - Are named similarly to straight chained alkanes. - The C in the ring that contain the double bond are always assigned the #1 and #2 positions, so numbers are used only to locate the positions of substituents attached to the ring – not to locate the position of the double bond. The general formula for cyclic alkenes CnH2n-2  Physical and Chemical properties of cycloalkenes: Physical state: Smaller cycloalkenes are gases, while larger ones are mostly liquids. Reactivity: Cycloalkenes are more reactive than cycloalkanes due to the double bond's increased electron density shifts.  Physical and Chemical properties of cycloalkenes: Boiling point: The boiling point of alkenes increases with the number of carbon atoms in the compound. Melting point: The melting point of alkenes depends on the positioning of the molecules. Polarity: Alkenes are weakly polar, but slightly more reactive than alkanes due to the double bonds. Alkynes  Contain one or more triple bonds  Unsaturated hydrocarbons  Structure with triple bond is linear  More reactive than the double bond  General formula CnH2n-2  Naming alkynes follow the same rules for alkenes - yne ( or diyne, -triyne) Properties of Alkynes The physical properties of alkynes resemble those of hydrocarbons having similar shape and molecular weight. Alkynes have low melting points and boiling points. Melting point and boiling point increase as the number of carbons increases. Alkynes are soluble in organic solvents and insoluble in water. Naming Alkynes Alkynes are named in the same general way that are alkenes are named. In the IUPAC system, change the – ane ending of the parent alkane name to the suffix – yne Choose the longest continuous chain that contains both atoms of the triple bond and number the chain to give the triple bond the lower number. Compounds with two triple bonds are called di- ynes, those with three are called tri- ynes and so forth. The simplest alkyne, H-C- C-H, named in the IUPAC system as ethyne, is more often called acetylene, the common name. The two carbon alkyl group derived from acetylene is called an ethynyl group. Do this: Draw the structure of the following a. 1,2 – dimethylcyclopentene b. 2-methyl-2-butene c. 3-ethylcyclopentene d. 2-methyl-1- pentene e. 2,3-dimethyl-4-octyne f. 3,3-dimethyl-1-butyne Do this: Write the condensed structure of the following: a. 4 – isopropyl octene b. 3,4- dimethyl-4-n propylheptene c. 3-ethyl-3-hexene d. octene e. Cyclopropyne f. 4,4-dimethyl-2-pentyne g. 3-nbutyl-2-ethylcyclohexene h. 3,4-diethyl-4,6-dimethyl nonyne