• The central atom is bonded to two and only two atoms.
• The electron states of the central atom have half 2s and half 2p character.
• Three atoms generally form a straight line.

Common SP (linear) Atoms

• Beryllium hydride (BeH2)   
• Beryllium fluoride (BeF2) 
• Carbon dioxide (CO2) 
• Hydrogen cyanide (HCN) 
• Acetylene (HCCH) 

SP2 Hybrid Atomic Orbitals

• Combination of two 2p orbitals with one 2s orbital gives three SP2 hybridized orbitals.
• These three orbitals generally lie in a plane.
• An orbital may be filled with a single/double bond, or a single/paired electron.

Common SP2 (trigonal planar) atoms

• Borane (BH3) 
• Boron trifluoride (BF3) 
• Formaldehyde (CH2O) 
• Ketones (>C=O) 
• Aldehydes (RCOH) 
• Alkenes (>C=C<) 
• Carbonate ion (CO32-) 
• Benzene (C6H6) 
• Graphite 
• Fullerenes 
• Nitrogen dioxide 
• Ozone (O3-)
• Sulfur dioxide (:SO2)
• Sulfur trioxide (SO3)

SP3 Hybrid Atomic Orbitals

• Combination of one s and three p orbitals, yielding four SP3 hybridized orbitals.
• Generally has shape of a tetrahedron.
• Often one or two orbital locations are filled with electron pairs (as in water).

Common SP3 (tetrahedral) atoms

• Methane (CH4)  
• Tetrafluoromethane (Carbon tetrafluoride) (CF4) 
• Tetrachloromethane (Carbon tetrachloride) (CCl4) 
• Chloromethane (Methyl chloride) (CH3Cl)
• Ammonium ion (NH4+) 
• Ammonia (:NH3) 
• Phosphorous tetrafluoride (:PF3) 
• Thionyl fluoride (:SOF2) 
• Water (H2O) (::OH2) 
• Sulfur difluoride (SF2) 

Here are some common nucleophiles used in organic chemistry SN1, SN2, E1, and E2 reactions, sorted by strength:

• VERY Good Nucleophiles: SH^-, RS^-, I^-
• Good Nucleophiles: CN^-, N3^-, Br^-, HO^-, RO^-
• Fair Nucleophiles: NH3, Cl^-, F^-, RCO2^-
• Weak nucleophiles: H20, ROH
• VERY Weak Nucleophiles: RCO2H

Let’s say we have a 5-carbon molecule with a ketone functional group. According to ketone nomenclature, the name will be pentanone. Pentan- for the 5 carbon chain, and -one for the ketone primary functional group.

But, the name pentanone doesn’t give us enough information to draw the molecule, because we don’t know where the ketone is on the carbon chain.

In this example, a locant can be used to specify where the ketone is attached. The above examples can be renamed 2-pentanone (top) and 3-pentanone (bottom).

If a compound has multiple functional groups, then a locant can be used for each one:

In this example, locants are used to show that a Bromine is attached to carbon #6, a methyl is attached to carbon #2, and the double bond starts at carbon #1.

Not all locants are numbers! When naming amides, the locant “N” is often used.

We are also obeying the normal rules of valence, (and this chart) there will be:

• 1 bond to each H
• 4 bonds to each C
• 2 bonds to each O

Here are 8 isomers I could think of. Can you find more?

The problem states that there cannot be any rings (non-cyclic constitutional isomers), so we know there must be 1 double bond in this 4-carbon molecule.

Here are the bond-line formulas of the 4 non-cyclic constitutional isomers of C4H8:

A molecule becomes unsaturated due to double bonds, triple bonds, and rings.

Given a molecular formula, you can calculate the degrees of unsaturation:

• C = # of carbons
• N = # of nitrogens
• X = # of halogens
• H = # of hydrogen

Each double bond or ring increases the molecule’s degree of unsaturation by 1. A triple bond increases the degree of unsaturation by 2.

Lewis structures are a way to use letters, dots, and lines to represent atoms, electrons, and bonds. 

Here is the Lewis structure for water:

Things to notice:

• The letter “O” represents oxygen, and the letter “H” represents hydrogen.
• The dots above the oxygen represent two lone pairs of electrons.
• The lines between “O” and “H” represent bonds between oxygen and hydrogen. Each bond requires 2 electrons.
• Oxygen follows the “Octet Rule”, and is drawn with 8 electrons around its valence shell (4 from the two lone pairs, and 4 from the two bonds).
• The hydrogens follow their special “Duet Rule”, and have 2 electrons around their valence shells (a single bond contains two electrons).

How to draw Lewis Structures

Each atom has a particular number of valence electrons available to start, determined by its position in the periodic table:

Let’s say we wanted to draw Carbon Dioxide, CO2.

• According to the above chart, Carbon has 4 starting valence electrons, and Oxygen has 6.
• Draw these electron dots around their atoms.
• If there are 4 valence electrons or less, they will all be single, unpaired electrons. Carbon has 4 single, unpaired electrons.
• If a molecule has 5 valence electrons, the 5th electron pairs up with the 1st single unpaired electron, resulting in 3 single electrons and 1 lone pair.
• If a molecule has 6 valence electrons (like oxygen), the 5th and 6th valence electrons pair up with the 1st and 2nd electrons to form 2 lone pairs. 
• 7 valence electrons = 3 lone pairs w/ 1 single unpaired electron.
• 8 valence electrons = 4 lone pairs w/ 0 single unpaired electrons.

• The number of single, unpaired electrons corresponds to the number of bonds each atom can make. In our example of carbon dioxide, above the carbon can form 4 bonds, and the oxygens can each form 2 bonds.
• Armed with our knowledge of the “Octet Rule” and the number of bonds each atom can take, we can finally draw our Lewis structure!

One of the most common questions in organic chemistry:

“How do I know if a reaction will be SN1/SN2/E1/E2?”

First question: what kind of halide are we dealing with?

• Methyl Halide: SN1 or SN2
• Primary Halide: SN2 or E2
• Secondary Halide: SN1, SN2, E1, or E2
• Tertiary Halide: SN1, E1, or E2

Methyl Halide

• SN2 is most favored, since carbocation (formed during SN1) would be very unstable.
• No E1 or E2, since it’s impossible to make a double bond!

Primary Halide

• If there is a strong nucleophile, SN2 is favored.
• E2 is favored if using a big, bulky base like t-butoxide (due to steric hindrance effects).

Secondary Halide

• SN2 is favored with strong nucleophile, at low temperature, and aprotic solvent.
• E2 is favored with strong nucleophile, high temperature, aprotic solvent, and big bulky bases.
• SN1 is favored with weak nucleophile, low temperature, and polar protic solvent.
• E1 is favored with weak nucleophile, high temperature, and polar protic solvent.

Tertiary Halide

• E2 is favored with strong nucleophile like OH(-) or OR(-).
• SN1 is favored with weak nucleophile, low temperature.
• E1 is favored with weak nucleophile, high temperature.

• Fluorine (F)
• Chlorine (Cl)
• Bromine(Br)
• Iodine (I)

The Jones Oxidation reaction involves reacting an alcohol (OH) with Chromic Acid (CrO3).

• 2° (Secondary) Alcohol -> Ketone
• Most 1° (Primary) Alcohol -> Carboxylic Acid
• 1° Allylic/Benzylic Alcohol -> Aldehyde

When reacting a 2° alcohol with chromic acid an intermediate chromate ester forms. This ester then reacts with a base (water), removing the Chromate portion and producing a ketone.