CHEM 2211 1st Edition Lecture 15 Outline of Last Lecture I Sterochemistry II Alkenes Outline of Current Lecture I Alkenes II Nomenclature for alkenes a R and S b E and Z Current Lecture Alkenes Are like alkanes except the contain a double bond This bond is formed by overlapping P orbitals Nomenclature for Alkenes I II III IV V VI The process for naming alkenes is similar to alkanes except orientation in space is considered with R an S and E an Z prefixes Select the longest parent chain containing the functional group alkene Number the chain with the alkene group getting the lowest possible number Assign the correct prefix name to the parent chain with the prefix ene for alkene Check for branching groups and name them accordingly Determine the orientation of center molecules R and S or E and Z Put it all together These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute If there is more than one alkene group in a chain Select the longest parent chain containing both alkenes Number the chain with the lowest possible numbers on the groups Put the location of the alkene groups separated by commas Then add the prefix of how many groups there are before the parent chain name o 2 di o 3 tri o 4 teta o Etc And add suffix ene to the end like usual What to do if all the alkenes cant be on the same chain 3 alkene groups but they all can t be in one chain Select the longest chain containing the greatest number of alkene groups possible circled Name that chain 1 3 hexdiene Then name the branching chain 2 C chain is usually ethyl 2 C chain with alkene group is ethenyl In cyclics double bond gets assigned the number one always Then determine which way to number the rest of the substituents with the lowest numbers Sterochemistry R S and E Z Naming alkene requires stereochemistry E and Z replaces cis and trans naming They can be compared to cis and trans E high energy atoms on opposite sides of the molecule trans Z high energy atoms on same side of the molecule cis E and Z are used when there are four different groups of atoms not just two groups of the same atoms like with cis and trans naming The four groups are assigned high and low priority to determine if the center molecule is E or Z High priority on same side is Z High priority atoms on different sides is E Example of E and Z atoms CH3CH2 CH3 C C CH3 CH2CH3 Priority can be best determined by using atomic mass high mass higher priority Assignment for above molecule High low Low high The high priority atoms are on opposite sides of the double C bond This means this molecule is E Name E 3 4 dimethyl 3 hexene
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