Chapter Eleven chemistry note

·         Alkenes and alkynes are families of hydrocarbons that contain double and triple bonds, respectively. They are called unsaturated carbons because they do not contain the maximum number of hydrogen atoms as do alkanes. They react with hydrogen gas to increase the number of hydrogen atoms to become alkanes, which are saturates hydrocarbons because they so have the maximum number of hydrogen atoms.

·         Alkenes contain one or more carbon-carbon double bonds formed when adjacent carbon atoms share two pairs of valence electrons.

·         In an alkyne, a triple bond forms when two carbon atoms share three pairs of valence electrons.

·         Naming alkenes and alkynes:

1.      Name the longest carbon chain that contains the double or triple bond. Replace the suffix with the respective new suffix, -ene or –yne.

2.      Number the longest chain from the end nearest the double or triple bond. Indicate using the lowest number. You have to name where the bond is.

3.      Give the location and name of each substituent in alphabetical order as a prefix to the alkene or alkyne name.

·         In alkenes, there is no rotation around the carbons in the double bond because it’s rigid.

·         A cis isomer, the hydrogen atoms are on the same side of the double bond.

·         Trans isomers have hydrogen atoms on opposite sides.

·         Cis or trans comes first when naming the group.

·         For alkenes and alkynes, the most characteristic reaction is the addition of atoms or groups of atoms to the carbons of the double or triple bond.

·         In a reaction called hydrogenation, two atoms of hydrogen atach to the carbons in a double bond of an alkene to form alkane.

·         In hydration, an alkene reacts with water (H-OH). The hydrogen atom forms a bond with one carbon atom in the double bond, and the oxygen atom in OH forms a bond with the other carbon.

·         When water adds to a double bond in which the carbon atoms are attached to a different number of H atoms, the H from HOH attaches to the carbon that already has the most H atoms.

·         Polymers are large molecules that consist of small repeating units called monomers.

·         Another hydrocarbon is benzene. Because many compounds containing benzene had a fragrant odor, the family of benzene compounds became known as aromatic compounds. A benzene molecule consists of a ring of six carbon atoms with one hydrogen atom attached to each carbon.

·         When a benzene ring is a substituent, it’s named as a phenyl group.