Organic Chemistry

Molecular formula

Formula that shows just the number of atoms of each element. Ex. C₅H₁₂

Condensed formula

Identifies the specific structural isomer by specifying the order of attachment of the atoms. Ex. CH₃CH₂CH₂CH₂CH₃

Wedge

Out of the page

Dash

Into the page

Constitutional (structural) isomers

Compounds with the same molecular formula but different connectivity of atoms.

Steric number

This is the number of electron domains, which can be either a lone pair or a bond. (cations and radicals do not contribute)

• sp³ has a steric number of 4

• sp² has a steric number of 3

• sp has a steric number of 2

Sigma bonds

Direct overlap of unhybridized ‘s’ orbitals and/or hybrid AOs form sigma bonds. Single bonds are composed of 1 sigma bond.

Pi bonds

Due to lateral overlap of unhybridized p orbitals. Double bonds are composed of 1 sigma bond and 1 pi bond. Triple bonds are composed of 1 sigma bonds and 2 pi bonds.

Molecular geometry for sp³

• Tetrahedral

  • It has 4 bonds, and 0 lone pairs.

  • Has an angle of 109.5

• Trigonal pyramidal.

  • Has 3 bonds and 1 lone pair.

  • It has an angle of <109.5

• Bent

  • It has 2 bonds and 2 lone pairs.

  • It has an angle of <109.5

Molecular geometry of sp²

• Trigonal planar

  • It has 3 bonds and 0 lone pairs.

  • It has an angle of 120.

• Bent

  • It has 2 bonds, and 1 lone pair.

  • The angle is <120

Molecular geometry for sp

It is linear. It has 2 bonds and 0 lone pairs. It forms a 180 angle.

Rules for determining most signifcant resonance contributor

1. Maximize the # of complete octets

2. Minimize the # of formal charges

3. A structure with negative charge on the more electronegative atom is more stable.

4. A structure with positive charge on the less electronegative atom is more stable.

Bronsted-Lowry Definition of Acids and Bases

A Bronsted-Lowry acid is a proton donor and a Bronsted-Lowry base is a proton acceptor.

Lewis definition

A Lewis acid is an electron pair acceptor and a Lewis base is an electron pair donor. Lewis acid is an electrophile, it wants an electron and donates a proton. Lewis base is a nucleophile, it wants a proton and will donate electron.

K_a and K_b

K_a is the acid dissociation constant. A strong acid has a high K_a and a weak acid has a low K_a. K_b is same idea, the stronger the base the higher the K_b. The weaker the base, the lower the K_b

pK_a and pK_b

K_a is inversely related to pK_a. So, strong acid has lower pK_a and weak acid has higher pK_a. A compound’s pK_a measures the stability of the compound’s conjugate base. As the stability of the conjugate base increases, the pK_a decreases.

The stronger the base the weaker the pK_b, and the weaker the base the higher the pK_b.

Deprotonation

This is a process where protons are lost. Both acids and bases become deportonated when pH > pKa. Acids will undergo deprotonation at a low pH. Bases will undergo deprotonation at a high pH or not at all.

Acid base equilibrium

Acid base reactions favor formation of the weaker acid (higher pKa). Strong acids product weak (stable) conjugated base. Strong bases produce a weak (stable) conjugate acid.

Ranking acidity.

Use acronym CARDIO in the exact order:

1. Charge: Acidity increases with increasing positive charge.

2. Atom: Acidity increases as we go down a column or across a row from left to right on a periodic table.

3. Resonance Delocalization: Resonance delocalization that increases the stability of a conjugate base will increase the acidity of a molecule.

4. Induction: Electronegative atoms on nearby carbons stabilize the conjugate base, making it more acidic.

5. Orbital Hybridization: If the atom being deprotonated has greater s character, it will be more acidic.

London Dispersion Forces (LDF)

Weakest intermolecular forces. Occur between all molecules, and they are the only attractive force experienced by non-polar molecules. Aris from momentary/insantaneous dipoles.

Dipole Dipole interactions

This is when oppositely charged dipoles on atoms from different molecules attract each other.

Hydrogen bonding

Occurs in fluorine, oxygen, or nitrogen when they are directly bound to hydrogen. They are strong dipole dipole interactions.

Ion Ion interactions

Occur between positively charged ions (cations) and negatively charged ions (anions). Strongest intermolecular forces.

Melting and boiling point

A molecule with strong intermolecular forces will have a high melting point and a high boiling point. Large molecules also have higher melting and boiling points. Increased branching decreases the boiling point. Increased molecular symmetry leads to a higher melting point.

Parent chain naming conventions

1. meth -

2. eth -

3. prop -

4. but -

5. pent -

6. hex -

7. hept -

8. oct -

9. non -

10. dec -

Alkane

Has no carbon-carbon double or triple bonds. Add the suffix “ane” to the parent chain. Parent chain should be numbered so substituents have lowest possible numbers.

Alkyl substituents

They are named with the same prefixes as the carbon chain, add “yl” to the end instead. If multiple present, list them in alphabetical order. If multiple of the same present, designate them with “di,” “tri” , “tetra” and “penta.”

Alkene

If the molecule has at least one carbon-carbon double bond, it is an alkene. It is named by adding -ene to the parent chain. (designate where it is with the number). Has higher priority than alkyl or halogen subsitutents.

Alkynes - “yne”

If the molecule has at least one carbon-carbon triple bond it is an alkyne. Named by adding -yne to the parent chain. Has higher priority than alkyl or halogen subsitutents.

Cyclic compounds

Cyclic alkanes are named with the prefix “cyclo.”

Spiro compounds

Compounds connected by two rings connected by a single carbon. To name:

• Count number of carbons in each ring, excluding the spiro center.

• List number from lowest to highest inside brackets.

• Add the prefix “spiro” before the brackets.

• Count the total number of carbons and write the alkane parent chain name after the brackets.

Bicyclic compounds

Compounds with two or more rings linked together by two bridgehead carbons. To name a bicylic compound:

• Count the number of carbons in each ring, excluding the bridgehead carbons.

• List the numbers from highest to lowest inside brackets.

• Add the prefix “bicyclo” before the brackets.

• Count the total number of carbons and write the alkane