What is Organic Chemistry?

Organic Chemistry is the study of carbon and its compounds

Carbon is unique among elements Each carbon nucleus contains six protons Each carbon atom has six electrons, but can share up to four more with other atoms The four outer electrons are available to make four covalent chemical bonds Carbon’s ability to share electrons with others is unmatched; The overwhelming majority of known compounds (substances with 2 or more elements) are carbon compounds

Carbon Electronic Structure Carbon’s electron configuration: 2-4 (1s22s22p2) Halfway to a complete valence shell Too many e- to lose, too many to gain Carbon’s strategy: share electrons with everybody!

Pure Carbon Pure carbon exists in a number of forms (allotropes)

Carbon is usually bonded to something else – other elements Favorite partners: hydrogen, oxygen, nitrogen

Carbon can make big molecules Carbon will form long chains with other carbon atoms The four outer (valence) electrons are shared between the carbon and the other atoms Because of the large number of bonds and the willingness of carbon to share electrons, there are millions of possible organic compounds

Structural Formulas Because of their complexity, carbon compounds are represented in a number of ways. CH4 Chemical Formula 3D structural formula Structural Formula Space-filling model

Carbon-Hydrogen Bonds Carbon and hydrogen share a pair of electrons, forming non-polar covalent bonds

Organic Nomenclature Millions of organic compounds need to be distinguished from one another The IUPAC system allows us to name the most common organic compounds with some practice We will work with sets of plastic models to build and name organic compounds

Representations of carbon compounds There are numerous ways to visually describe carbon compounds The most common are “ball and stick” models Our models represent the shared electron pair as a grey stick These models show the three-dimensional shapes of molecules very well “Space filling” models are also used: they are more accurate, but less useful

Model Types ball and stick space filling

Carbon and Hydrogen Hydrogen is carbon’s favorite partner Hydrogen is smaller than carbon: a single proton and electron Carbon and hydrogen share a pair of electrons equally, making a single covalent chemical bond Compounds of carbon and hydrogen are called hydrocarbons Liquid hydrocarbons have a very high “energy density,” and are basis for the global economy

Naming Hydrocarbons Hydrocarbons are the simplest organic compounds. Hydrocarbon names have prefixes based on the longest continuous chain of carbons. This is one of your chemistry reference tables:

Naming simple hydrocarbons Straight chain hydrocarbons that contain only single bonds are called alkanes. Alkanes have the suffix –ane on the end of a name. Alkanes can be straight chains or carbons, or branched; we’ll start with the straight ones:

Name These Alkanes What is the chemical formula for heptane?

Alkanes: a homologous series of hydrocarbons All alkanes have the general formula CnH2n+2

Isomers After three carbons, branched hydrocarbons become common. Butane has two possible compounds, called isomers. Isomers have the same chemical formula, but different structural formulas. Butane and “iso-butane” have different physical properties.

Properties of Butane Isomers Boiling point: 0.5⁰C Boiling point: -10⁰C Iso-butane is now a common referigerant, despite the fact that it is potentially explosive. It has replaced CFCs (chlorofluorcarbons), which destroy ozone.

Common names and IUPAC names The most important organic compounds often have common names that you may have heard of… Formaldehyde ethylene iso-butane ethylene glycol acetic acid We will be learning the official nomenclature, called the IUPAC system.

Naming iso-butane methyl propane 2- Count the longest continuous carbon chain – called the parent chain. Be sure you have the longest chain – looks are deceiving!! Name the parent chain using the prefixes. Count the carbons in the parent chain and number each one. Look for a branch. A one-carbon branch is called a methyl group. Note the carbon number where the group is found. methyl propane 2-

Name these pentane isomers When more than one branch is present, each one needs to be named individually, with its location on the parent as part of the name. Another set of prefixes: di, tri, tetra, penta, etc. are used to indicate how many branches there are.

Condensed Structural Formulas

Larger hydrocarbons have lots of isomers! The larger the hydrocarbon, the more possibility for isomers. For example, heptane has eleven isomers:

Physical Properties of Hydrocarbons Hydrocarbons are non-polar compounds. Carbon and hydrogen share electrons more or less equally Hydrocarbons have relatively low melting points and boiling points: the four smallest are gases at room temperature The intermolecular attraction between molecules increases as the number of carbons increases

Separating Mixtures of Hydrocarbons in Crude Oil

Boiling Points of Alkanes Boiling Point (°C) Heptane 98.5 Propane -42 Pentane 36 Butane 0.5 Methane -161 Ethane -88.5 Hexane ? Be sure to unscramble these: they are not in sequence!!

Name the following:

Draw structural formulas for: 2, 3 dimethyl pentane 2-methyl hexane 3-ethyl hexane heptane