Organic Chemistry The study of the structure, reaction, and synthesis of compounds that consist mostly of carbon and hydrogen Organic compounds can contain other elements, such as nitrogen, oxygen, halogens, and sulfur in smaller amounts It is important to elucidate the structure and bonding of the atoms in organic compounds to help understand how and why they react Carbon atoms generally bond covalently, sharing one, two, or three pairs of electrons with other atoms To do this, they use either sp3 (tetrahedral), sp2, (trigonal planar), or sp (linear) hybridization schemes

sp3 Hybridization: 1 s and 3 p AOs combine to form 4 sp3 hybrids Useful for describing tetrahedral geometry around a carbon atom 1s bond 109.5° bond angles 413 kJ/mol 1.54 Å sp2 Hybridization: 1 s and 2 p AOs combine to form 3 sp2 hybrids Useful for describing trigonal geometry around a carbon atom 1s bond / 1p bond 120° bond angles 614 kJ/mol 1.34 Å sp Hybridization: 1 s and 1 p AOs combine to form 2 sp hybrids Useful for describing linear geometry around a carbon atom 1s bond / 2p bonds 180° bond angles 839 kJ/mol 1.20 Å

Bonds that form between atoms with different electronegativities are polar covalent bonds Electronegativity increases as you move up through a group and right through a period on the periodic table C - C DEN = 2.5 – 2.5 = 0 Non-polar C - H DEN = 2.5 – 2.1 = 0.4 Slightly polar C - O DEN = 3.5 – 2.5 = 1.0 Polar C - F DEN = 4.0 – 2.5 = 1.5 Very polar If polar bonds are present in a molecule, and the molecule is asymmetric, it will be a polar molecule Non-polar Polar Polar Non-polar

Different interactions lead to different reaction mechanisms Polar molecules have a separation of charge and they will interact electrostatically Cl- H d+ C F d- H H Molecules with regions of high electron density will behave in a similar way H+ + H H C C H H H It is interactions like this that lead to reactivity in organic molecules Different interactions lead to different reaction mechanisms

Organic molecules that contain carbon and hydrogen Hydrocarbons Organic molecules that contain carbon and hydrogen Saturated Hydrocarbon Unsaturated Hydrocarbon Hydrocarbons are identified and named primarily by the number of carbons if their longest carbon chain Chain length is denoted using prefixes 1 C meth- 5 C pent- 2 C eth- 6 C hex- 9 C non- 3 C prop- 7 C hept- 10 C dec- 4 C but- 8 C oct-

The type of hydrocarbon is given by the level of saturation Alkanes All CH bonds are single bonds Formula: CnH2n+2 CH4 methane C3H8 propane C6H14 hexane C2H6 ethane C4H10 butane C8H18 octane Alkenes Contain double bonds Formula: CnH2n C2H4 ethene ethylene C4H8 butene butylene C3H6 propene propylene C6H12 hexene hexylene Alkynes Contain triple bonds Formula: CnH2n-2 C2H2 ethyne ethylyne C4H6 butyne butylyne C3H4 propyne propylyne C6H10 hexyne hexylyne

If there are substitutions on the longest chain, the carbons are numbered to identify the location of the substitution Substitution = - CH3 methyl group 1 2 3 4 5 6 CH3 CH2 Hexane CH3 CH CH2 2- methylhexane CH3 CH2 CH 3- methylhexane CH3 CH2 C 3,3 - dimethylhexane CH3 CH2 CH 3,4 - dimethylhexane

For alkenes, the numbering system is used to locate the double bond(s) 1 - pentene If there is more than one double bond, we use the term diene 1,4 - pentadiene We can combine these rules for molecules with multiple items 2,2 – dimethyl – 3-hexene

When the double bond is on a middle carbon, we have to worry about which “side” of the double bond is substituted trans - 2 - butene cis - 2 - butene 1 8 3 – octene 2 7 5 6 – 6 methyl 3 4 cis – Cis - 6 – methyl – 3 - octene

The terminal carbons can bond to each other to make rings Cyclic compounds The molecules are very floppy because they can rotate around the C-C bonds The terminal carbons can bond to each other to make rings cyclo hexane This molecule is best viewed in three dimensions

If we make the molecule unsaturated, an aromatic compound may result benzene Resonance structures There is actually overlap between all of the unhybridized p-orbitals on each sp2 carbon atom The actual benzene molecule is a hybrid of these resonance structures, with a 50% contribution from each

Each carbon in the ring is sp2 hybridized so they have 3 sp2 hybrids and one unhybridized atomic p-orbital H H H H H H Two sp2 hybrids on each carbon overlap to form s bonds The 3rd sp2 hybrid on each carbon overlaps with H to form a s bond All p-orbitals overlap side-to-side to make p-bonds

Functional groups Functional groups are specific groupings of atoms that are responsible for the characteristic reactivity of different compounds The presence of different functional groups add to the naming scheme for organic molecules There is a formal name for each molecule, but there are also common names New and different types of substitution are possible with different groups on the carbon chains

Halogenated Hydrocarbons Formula: R-X R = organic molecule X = halogen Chloromethane Bromoethane trans-Dichloroethene ortho - Difluorobenzene meta - Difluorobenzene para - Difluorobenzene

Alcohols Formula: R-OH Methyl alcohol Methanol Ethyl alcohol Ethanol trans - 1,2 - ethylenediol o -Benzenediol m -Benzenediol p -Benzenediol Catechol Resorcinol Hydroquinone

trans - 1,2 - dimethoxyethene Ethers Formula: R-O-R Dimethyl Ether Diethyl Ether trans - 1,2 - dimethoxyethene o -Dimethoxybenzene m -Dimethoxybenzene p -Dimethoxybenzene

Formula: R – C - H O Aldehydes Acetaldehyde Benzaldehyde Formaldehyde Formula: R – C – R’ O Ketones Acetone Methyl ethylketone Methyl phenylketone

Formula: R – C - OH O Carboxylic Acids Formic Acid Acetic Acid Benzoic Acid Formula: R – C – O- R’ O Esters Methyl Acetate Ethyl Acetate

Acetic Anhydride Salicylic Acid Acetic Acid Acetylsalicylic Acid