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Organic Chemistry by Brown, Iverson, Anslyn, Foote | Mayya's Study Guide | Chapter 5

Chapter 5 Alkenes: Bonding, Nomenclature, and Properties


Table of contents of main topics:

Structure of Alkenes

Alkenes are hydrocarbons that contain one or more carbon-carbon double bonds. Alkenes are considered unsaturated hydrocarbons (a molecule that has one or more carbon-carbon double or triple bonds.


How to calculate Index Of Hydrogen Deficiency (IHD) (degree of unsaturation)
How to calculate Index Of Hydrogen Deficiency (IHD) (degree of unsaturation)

One degree of unsaturation means the molecule has either a ring or a double bond. Two degrees of unsaturation means the molecule has either two double bonds or two rings or a double bond and a ring or a triple bond. If there is four or more degrees of unsaturation there is a high chance for a benzene ring since it has 4 degrees of unsaturation (one ring and three double bonds).

For example, if the formula is C2H4, we do (2*2+2-4)/2 = 1. This molecule must have one degree of unsaturation.


Cis,Trans Isomerism in Alkenes



Nomenclature of Alkenes


1. Find the longest continuous carbon chain (can be vertical, horizontal, etc) containing the double bond. The name of the parent chain will start with a prefix signifying the number of carbons in the chain and end with "ene". Start counting from the end closest to the double bond to give double bond the lowest number possible.






2. Name the substituents same as in alkane naming.




The E/Z System


Mayya's Trick

  1. Break the double bond in half and look at each half separately (don't look at the other half).

  2. Find two groups the carbon on the double bond is attached to (if only one group is shown, the other must be hydrogen).

  3. Identify the highest priority atom based on the atomic number. If two atoms are the same, keep going atom by atom until the first point of difference (like R/S rules).

  4. Once you are done with both carbons, see if the two highest priority groups are on the same side of the double bond(Z) (Z-zame,same) or on the oppposite side of the double bond (E)


E,Z system naming
E,Z system naming

Naturally Occurring Alkenes—Terpene Hydrocarbons


isoprene structure
isoprene structure

Terpene is a compound made up of isoprene units. Terpenes are formed by bonding tail of one isoprene unit to the head of the other.


terpene examples
terpene examples

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