Chapter 20
All organic compounds contain carbon, however, not all carbon containing compounds are classified as organic. Organic compounds covalently bonded compounds containing carbon, excluding carbonates and oxides. Organic chemistry is the study of these compounds. Carbon gets its own branch of study because of the diversity of compounds that it can form.
There are more compounds of carbon than there are of all the other elements on the periodic table combined.
All carbon has six protons and six electrons Naturally occurring carbon has three isotopes C-12, C-13, and C-14 C-12 is by far the most abundant so average atomic mass is very close to 12.000 amu Carbon has an electron configuration of 2-4 or 1s 2, 2s 2, 2p 2 It has four valence electrons Typically forms four bonds in an attempt to achieve the octet
Carbon can form these four bonds in a variety of ways Carbon can bond in multiple ways to other elements Can also bond to form long chains and rings
Simplest organic compounds are called hydrocarbons Hydrocarbons are composed only of carbon and hydrogen.
Alkanes are hydrocarbons that contain only C-C single bonds. Simplest alkane contains one carbon. Formula is CH 4 and compound is called methane. Prefix indicates the number of carbons in the molecules and the suffix indicates the type of hydrocarbon it is.
A two carbon alkane is called ethane. Formula is C 2 H 6
A three carbon alkane is called propane. Formula is C 3 H 8
A four carbon alkane is called butane. Formula is C 4 H 10
Isomers compounds that have the same formula but a different structure.
How many different isomers can you draw for pentane, C 5 H 12?.
How many different isomers can you draw for hexane, C 6 H 14?.
Systematic Naming of Alkanes Historically, the names of many organic compounds were derived from the sources in which they were found Some of these names still persist today As more organic compounds were discovered, the need for a systematic naming system became apparent Five ways of drawing C 6 H 14 Can t call them all hexane Although they have similar chemical properties, they have different physical properties and are different molecules
Systematic Naming of Alkanes 1. Locate the longest unbroken C-C chain in the molecule and name it. 2. Number the chain starting from the end that gives the lowest possible sum of numbered carbons to which side chains are attached. 3. Name the side chains by using a prefix indicating the number of carbons in the side chain and using a yl suffix. 4. Put all pieces of the name together.
Name the different isomers of hexane, C 6 H 14.
Alkanes are hydrocarbons that contain the maximum number of hydrogen atoms Therefore they are saturated with hydrogen Unsaturated hydrocarbons exist when two carbon atoms are connected with either a double or triple bond Alkenes are hydrocarbons that contain a carbon-carbon double bond Alkynes are hydrocarbons that contain a carbon-carbon triple bond
Alkenes are hydrocarbons that contain a carbon-carbon double bond General formula is C N H 2N Naming system is consistent with that used for alkanes
Alkynes are hydrocarbons that contain a carbon-carbon triple bond General formula is C N H 2N-2 Naming system is consistent with that used for alkanes and alkenes
Aromatics hydrocarbons are hydrocarbons with sixmembered rings and delocalized electrons (resonance) Benzene is the primary aromatic hydrocarbon Formula of benzene is C 6 H 6
Hydrocarbons are non-polar molecules The only IMFs between these molecules are London s dispersion forces The strength of London s forces increases as the size of a molecule s electron cloud increases Molecular Formula IUPAC Name Boiling Point ( C) State at 25 C CH 4 methane -164 Gas C 3 H 8 propane -42.1 Gas C 4 H 10 butane -0.5 Gas C 5 H 12 pentane 36.1 Liquid C 8 H 18 octane 125.7 Liquid C 10 H 22 decane 174.1 Liquid C 17 H 36 heptadecane 301.8 Solid
Petroleum is a complex mixture of different hydrocarbons that varies greatly in composition Hydrocarbons in petroleum contain from one to fifty carbon atoms In fractional distillation, the components of a mixture are separated on the basis of boiling point
Alkanes are less reactive than other hydrocarbons because of the stability of their single covalent bonds One reaction they do undergo is combustion C 3 H 8 + O 2 CO 2 + H 2 O C 8 H 18 + O 2 CO 2 + H 2 O Combustion reactions are exothermic (- H) Heats of combustion values can be found on Table I
Engines can be powered by the combustion of gasoline Straight-chained hydrocarbons have more of a tendency to ignite spontaneously than branch-chained hydrocarbons This tendency is the basis for the octane rating scale The octane rating of a fuel is a measure of its burning efficiency and antiknock properties Octane rating scale is based on mixtures of heptane and 2,2,4- trimethylpentane Pure heptane burns with an octane rating of zero and pure isooctane burns with a rating of 100
Hydrocarbons can undergo reactions in which either add or substitute new atoms into the molecules Alkanes, which are saturated, can undergo substitution with halogens
Alkenes, which are unsaturated, can undergo addition with halogens or other small molecules.