HYDROCARBONS Since carbon atoms have 4 valence shell electrons they can easily form bonds at four locations with other atoms of carbon, hydrogen, oxygen, and halogens. One of the more common families of compounds have carbon atoms bonded to each other, end to end, with H atoms bonded at the remaining locations. These compounds of carbon and hydrogen are known as hydrocarbons.

When no double or triple bonds between adjacent carbon atoms exist the compounds have a maximum number of hydrogen atoms on the carbon chain and are called saturated hydrocarbons. This family of hydrocarbons are called the ALKANES and are named for the number of carbon atoms in the chain. The basic formula is CnH2n+2. Here is an example

C H For simplicity the pairs of electrons are usually represented by sticks which represent covalent bonds H C

Alkanes Saturated hydrocarbons are named Alkanes with the number of carbons in the chain determining the beginning of the name, while the end of the name is _______ane

H C H C H C 1 carbon methane CH4 2 carbons ethane C2H6 3 carbons propane C3H8

4 carbons butane C4H10 C H 5 carbons pentane C5H12 C H

6 carbons hexane C6H14 C H 7 carbons heptane C7H16 C H

8 carbons octane C8H18 C H 9 carbons nonane C9H20 C H

10 carbons decane C10H22 C H Since hydrogen atoms are assumed to fill all spot around the C atoms they are sometimes left out. These are called carbon skeleton diagrams. An example of a carbon skeleton diagram for hexane could be:

C - C - C | C - C C or C - C - C - C - C - C It is important to note that chains of C atoms do not have to be drawn horizontally. As long as they are drawn in a continuous string each C atom can be bonded to an adjacent C atom in any of the 3 remaining places

If this is the beginning of an 8 carbon chain The next carbon atom can go here C | Or here Or here C - C - C | C This can lead to a multitude of possible 2 dimensional drawings for the same molecule. Here are just a few of the possibilities for octane Or here

C - C | C - C - C - C C - C - C | C - C C Remember each C atom has 2 H atoms bonded to it, with an additional H atom bonded to the C atom at each end of the chain C - C | C | C - C - C C - C - C - C

Alkenes Some hydrocarbons have adjacent carbon atoms with double bonds. This reduces the number of hydrogen atoms bonded to the carbon chain by 2 hydrogens. These hydrocarbons are named Alkenes with the number of carbons in the chain determining the beginning of the name, while the end of the name is _______ene

C H Notice when adjacent carbon atoms use 2 additional electrons to form the 2nd bond there are 2 fewer places for H atoms to bond. This reduces the number of H atoms by 2 creating the general formula CnH2n C H

H C H C H C 2 carbons ethene C2H4 3 carbons propene C3H6 4 carbons butene C4H8 H C

Notice when the carbon chain reaches a length of 4 carbons, the double bond can be placed between the end carbons or the middle carbons. H C 1 2 3 4 Each of these structures is a different hydrocarbon. The top one is called 1-butene and the bottom one is called 2-butene. This naming method numbers the carbon skeleton chain in a way which encounters the double bond with the lowest possible number. H C 1 2 3 4

Isomers are compounds with the same formula but different structures. C5H10 is called pentene. How many different pentenes are there?

H C 1-pentene H C 2-pentene H C 3-pentene is the same as 2-pentene

Draw all possible hexenes, heptenes, octenes, nonenes and decenes. 3-decene, 4-decene, 5-decene

1-hexene 2-hexene 3-hexene

Isomers 1-heptene 2-heptene 3-heptene

Isomers 1-octene 2-octene 3-octene 4-octene

Isomers 1-nonene 2-nonene 3-nonene 4-nonene

Isomers 1-decene 2-decene 3-decene 4-decene 5-decene

Alkenes can have multiple double bonds Alkenes can have multiple double bonds. If they have 2 double bonds they are called dienes, 3 double bonds - trienes, 4 double bonds tetraenes, etc. Draw a diagram for propadiene. C H What is the name of this C Is it 3,4,7 -octatriene or 1,4,5 - octatriene Which starts with the lowest numbers?

Alkynes Some hydrocarbons have adjacent carbon atoms with triple bonds. This reduces the number of hydrogen atoms bonded to the carbon chain by 4 hydrogens. These hydrocarbons are named Alkynes with the number of carbons in the chain determining the beginning of the name, while the end of the name is _______yne

C H Draw a diagram for 2-pentyne. Remember the carbon chain can be numbered from left to right or right to left as long as the lowest possible numbered carbon begins the triple bond. In general what would be the formula for alkynes? CnH2n-2

Location of triple bonds 2 triple bonds alkyne What is the name of this structure? 1,3-hexadiyne 6 carbons Location of triple bonds 2 triple bonds alkyne

Draw a structural diagram, showing all atoms, for 2,4,6-nonatriyne.

Cyclic Hydrocarbons Carbon chains can also be bent back on themselves to form a closed chain. When this happens 2 hydrogen atoms are lost.

C H Name? cycloheptane If these 2 carbons bond together 2 hydrogen atoms must be removed

Construct the diagram for 1,3,5 - cyclohexatriene C C C H Or

Benzene as a side chain is named This structure is so common, it is given its own name, Benzene, and is usually drawn this way since further analysis has revealed the bonds between C atoms are neither single or double bonds but something in between. It is believed all the carbon atoms and hydrogen atoms in this ring share the electrons equally Benzene as a side chain is named phenyl

Name this structure. cyclopentene Name is 1,4-cyclooctadiene

Draw structural diagram showing all H atoms for 1,4-cycloheptadiyne Name 1,3,5-cyclohexatriyne