8.6 Naming and Drawing Alkenes Flashcards
what are alkenes
Hydrocarbons with 1 or more double bonds between carbon atoms are called Alkenes
what is the other name for alkenes
They are also called unsaturated carbohydrates because the carbons involved in the double bonds are holding fewer hydrogen atoms than they would in a single bond.
what is the simplest alkene
The simplest alkene is called ethene (C2H4). In an ethene molecule, two carbons are connected by a double bond, leaving four bonds for hydrogens. Ethene is used in making polyethene (polyethylene) for plastic bottles, plastic wrapping, and other plastic articles. The process involves adding many ethene molecules together in a polymerization reaction.
what are two important characteristics of double bonds
- The hydrogen atoms lie in the same plane.
- The double bond prevents free rotation. The atoms are in fixed positions.
what is the difference in reactivity between alkanes and alkenes
Though double bonds are strong than a single bond, it is easier to break one bond of a double bond, than to break the only bond of a single bond. which makes alkenes more reactive than alkanes
what is the ending of all alkenes
“ENE”
what is the alkene with 3 carbons
Propene (C3H6) has three carbon atoms and one double bond. It is used to make plastic pipes, bottles, sheets, carpets, etc.
what is the alkene with 4 carbons
Butene C4H8
what are isomers of butene
has two structural isomers, depending on where the double bond occurs. To find which isomer it is start numbering at the end closer to the double bond for alkenes. The double bond takes precedence over alkyl branches when numbering the carbons in an alkene. The position of the double bond is indicated by the number of the carbon atom that starts the double bond and is illustrated by the names 1-butene (double bond starts on carbon 1) and 2-butene (double bond starts on carbon 2)
what is the general formula for alkene formulas
The general formula for an alkene is CnH2n
what are the two versions of an alkene isomer
Alkene isomers like butene can be considered either “cis” or “trans” based on where the single hydrogen atoms attached to the two double bonding carbon atoms are.
when is an isomer Cis/Trans
If both hydrogen atoms are placed on the same side of a carbon chain, the molecule is considered “cis” ex cis-2-butene
If they hydrogen atoms are placed on opposite sides of the carbon chain, the molecule is considered “trans” ex trans-2-butene
why is an isomer being cis/trans important
Since the chain cannot rotate about the double bond, one form has quite distinct properties from the other. For example, their melting points are thirty degrees apart, and chemists exploit this fact to separate one isomer from the other.
what do you do if the substituents on either side of the bond are not identical, in determining cis/trans/neither
When the substituents on either side of the double bond arenotidentical we still need a way to determine cis and trans. What you look at is the molecular weight of the first atom attached to the carbon’s that form the double bond.
If Both heavier groups are on top or on the bottom, than it is cis
If the heavier groups are opposite, it is trans
what are the main difference between naming alkenes and alkanes
for alkenes Number the carbon chain starting on whichever side has the double bond on the lowest possible carbon. If the double bonds don’t have a preferred direction look to the groups.
Then determine if it’s a cis, trans, or neither type of isomer
