Organic Chemistry

Alcohols Nomenclature

Alcohols Nomenclature

Suffix -ol

Alcohols with two hydroxyl groups are called diols or glycols and are indicated with the suffix -diol

Aldehydes Nomenclature

Suffix -al

Methanal: Formaldehyde

Ethanal: Acetaldehyde

Propanal: Propionaldehyde

Ketones Nomenclature

Suffix -one

Carboxylic Acid Nomenclature

Suffix -oic acid

Esters Nomenclature

___ -yl ____-oate

Amide Nomenclature

Suffix -amide

Anhydride Nomenclature

Replace acid with anhydride

Isomer

Same molecular formula but different structures

Constitutional (Structural) Isomers

Same molecular formula/weight

Stereoisomer

Same structural backbone, differ in how atoms are arranged in space

Conformational Isomer

Differ in rotation around single bonds

Configurational Isomer

Can be interconverted only by breaking bonds

Newman Projection

A molecule is visualized along a line extending through a carbon-carbon bond axis

Staggered Conformation

When two functional groups in a Newman projection are oriented 180 degrees away from each other; AKA lowest-energy state

Anti Conformation

In a Newman projection, when the two largest groups are antiperiplanar (in the same plane, but on opposite sides) to each other; Occurs in a staggered conformation

Gauche Conformation

In a Newman projection, when the two largest groups are 60 degrees apart; Occurs in a staggered conformation

Eclipsed Conformation

In a Newman projection, when two methyl groups are 120 degrees apart and overlap with the hydrogen atoms on the adjacent carbon

Totally Eclipsed Conformation

In a Newman projection, when two methyl groups directly overlap each other with 0 degrees of separation; The molecule’s highest-energy state

Torsional Strain

Occurs when cyclic molecules must assume conformations that have eclipsed or gauche interactions

Nonbonded Strain (van der Waals Repulsion)

Results when nonadjacent atoms or groups compete for the same space; Dominant source of steric strain in the flagpole interactions of the cyclohexane boat conformation

Axial

In the chair conformation, the hydrogen atoms that are perpendicular to the plane of the ring (sticking up or down)

Equatorial

In the chair conformation, the hydrogen atoms that are parallel to the plane of the ring (sticking out)

Diastereomers

When two molecules are chiral and share the same connectivity but are not mirror images of each other because they different at some of their multiple chiral centers

For any molecule with n chiral centers, there are 2ⁿ possible stereoisomers

Optical Activity

When a chiral compound has the ability to rotate plane-polarized light; One enantiomer will rotate plane-polarized light to the same magnitude but in the opposite direction of its mirror image; Racemic mixtures don’t have this; Molecules with this lack a plane of symmetry

Dextrorotatory (d-)

A compound that rotates the plane of polarized light to the right, or clockwise; Labeled (+); Determined experimentally

Levorotatory (l-)

A compound that rotates light toward the left, or counterclockwise; Labeled (-); Determined experimentally

Specific Rotation

Racemic Mixture

When both (+) and (-) enantiomers are present in equal concentration; No optical activity is observed

Cis-Trans Isomers

Type of diastereomer in which substituents differ in their position around an immovable bond, such as a double bond, or around a ring structure, such as a cycloalkane in which the rotation of bonds is greatly restricted; In simple compounds with only one substituent on either side of the immovable bond, we use the terms cis and trans

Meso Compound

A molecule with chiral centers that has an internal plane of symmetry

Relative Configuration

The configuration of a chiral molecule in relation to another chiral molecule

Absolute Configuration

The exact spatial arrangement of atoms or groups in a chiral molecule, independent of other molecules

Cahn-Ingold-Prelog Priority Rules (E and Z Forms)

The alkene is named (Z) if the two highest-priority substituents on each carbon are on the same side of the double bond and (E) if they are on opposite sides

The higher the atomic number, the higher the priority

(R) and (S) Nomenclature

• Step 1: Assign Priority

Higher atomic number = Higher priority

• Step 2: Arrange in Space

Orient the molecule in 3D so that the atom with the lowest priority is at the back of the molecule (Anytime two groups are switched on a chiral carbon, the stereochemistry is inverted; if we switch the lowest-priority group to the back, we need to switch our final answer from (R) to (S), or vice versa)

• Step 3: Draw a Circle

Draw a circle connecting the substituents from 1-3

Counterclockwise = (S)

Clockwise = (R)

S-Orbital

Spherical and symmetrical, centered around the nucleus

P-Orbital

Composed of two lobes located symmetrically about the nucleus and contains a node—an area where the probability of finding an electron is zero—at the nucleus

D-Orbital

Composed of four symmetrical lobes and contains two nodes; Four of these orbitals are clover-shaped, and the fifth looks like a donut wrapped around the center of a p-orbital

Molecular Orbitals

When two atomic orbitals combine

Bonding Orbital

Produced when the signs of the wave functions of two atomic orbitals are the same; Lower-energy and more stable

Antibonding Orbital

Produced when the signs of the wave functions of two atomic orbitals are different; Higher-energy and less stable

Single Bonds

All of these are sigma bonds, accommodating two electrons; Requires more energy to break this than one of the two bonds in a double bond

Double Bond

One pi bond on top of an existing sigma bond; Hinders free rotation of atoms around the bond axis; Shorter than a single bond

Hybrid Orbitals

Formed by mixing different types of orbitals

S Character

Example Problem: an sp³ orbital has 25% s character and 75% p character

Lewis Acid

Electron acceptor

Lewis Base

Electron donor

Bronsted-Lowry Acid

A species that can donate a proton

Bronsted-Lowry Base

A species that can accept a proton

Amphoteric

Molecules that can act as either Bronsted-Lowry acids or bases

K_a Equation

pK_a

pK_a Values

Generally, bond strength decreases down the periodic table, and acidity therefore increases; The more electronegative an atom, the higher the acidity

Nucleophiles

Good _____ tend to be good bases

Nucleophilicity determined by:

• Charge: Nucleophilicity increases with increases electron density (more negative charge)

• Electronegativity: Nucleophilicity decreases as electronegativity increases because these atoms are less likely to share electron density

• Steric Hindrance: Bulkier molecules are less nucleophilic

• Solvent: Protic solvents can hinder nucleophilicity by protonating the _____ or through hydrogen bonding

In polar protic solvents, nucleophilicity increases down the periodic table (I- > Br- > Cl- > F-). In polar aprotic solvents, nucleophilicity increases up the periodic table (F- > Cl- > Br- > I-). In aprotic solvents, nucleophilicity relates directly to basicity.

Electrophiles

Species with a positive charge or positively polarized atom that accepts an electron pair when forming new bonds with a nucleophile; Almost always act as Lewis acids in reactions; Greater degree of positive charge increases electrophilicity

Anhydrides > Carboxylic Acids and Esters > Amides

Heterolytic Reactions

Reactions where a bond is broken and both electrons are given to one of the two products; Weak bases are more stable with an extra set of electrons and therefore make good leaving groups (conjugate bases of strong acids like I-, Br-, and Cl-)

S_N1 Reactions

Two steps; First step is the rate limiting step in which the LG leaves, generating a positively charged carbocation; The nucleophile then attacks the carbocation, resulting in the substitution product; Formation of the carbocation is the rate-limiting step (rate = k[R-L], where R-L is an alkyl group containing a LG); First order reaction; Planar intermediate; Product will usually be a racemic mixture

S_N2 Reactions

One step; The nucleophile attacks the compound at the same time as the LG leaves; Concerted, bimolecular reaction because the single rate-limiting step involves two molecules; Backside attack; Nucleophile must be strong, and the substrate cannot be sterically hindered (less substituted carbon = more reactive)

Rate = k[Nu][R-L]

Inversion of relative configuration; If the nucleophile and LG have the same priority in their respective molecules, this inversion will also correspond to a change in absolute configuration from (R) to (S); Stereospecific reaction where the configuration of the reactant determines the configuration of the product

Won’t occur with tertiary substrates

Oxidation State

An indicator of the hypothetical charge that an atom would have if all bonds were completely ionic

Oxidation Reaction

This type of reaction tends to feature an increase in the number of bonds to oxygen, and oxidizing agents often contain metals bonded to a large number of oxygen atoms

Reduction Reaction

This type of reaction tends to feature an increase in the number of bonds to hydrogen, and reducing agents often contain metals bonded to a large number of hydrides

Chemoselectivity

The preferential reaction of one functional group in the presence of other functional groups

Reaction Locations

A redox reagent will tend to act on the highest-priority functional group; For a reaction involving nucleophiles and electrophiles, reactions also tend to occur at the highest-priority functional group because it contains the most oxidized carbon; A nucleophile is looking for a good electrophile, the more oxidized the carbon, the more electronegative groups around it, and the larger partial positive charge it will experience; Aldehydes are generally more reactive toward nucleophiles that ketones; Carbon of a carbonyl

Pyridinium Chlorochromate

Weak oxidizing agent (PCC); Can oxidize primary and secondary alcohols

Polar Protic and Aprotic Solvents

PCC (Pyridinium Chlorochromate)

Oxidizing agent; Is the only oxidizing agent that can oxidize primary alcohols to aldehydes (does not oxidize the aldehyde)

Primary Alcohols

Oxidized into an aldehyde by PCC; Oxidized into a carboxylic acid by stronger oxidizing agents (i.e. chromium)

Secondary Alcohols

Can be oxidized to ketones by PCC or any stronger oxidizing agent

Tertiary Alcohols

Cannot be oxidized because they are already as oxidized as they can be without breaking a carbon-carbon bond

Jones Oxidation

CrO₃, dilute sulfuric acid, and acetone oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones

Mesylate

A compound containing the functional group -SO₃CH₃; Better LG that hydroxyl; Removed using a strong acid

Tosylates

Contain the functional group -SO₃C₆H₄CH₃; Better LG than hydroxyl; Removed using a strong acid

Acetals

Primary carbons with two -OR groups and a hydrogen atom; Not as reactive to reducing agents as carbonyls

Ketals

Secondary Carbons with two -OR groups; Not as reactive to reducing agents as carbonyls

Deprotection

Reverts an acetal or ketal back to a carbonyl with aqueous acid

Quinones

Produced by treating phenols with oxidizing agents

Hydroxyquinones

Quinones can be further oxidized to form these; Share the same ring and carbonyl backbone as quinones, but also have 1+ hydroxyl groups; Slightly less electrophilic than quinones