Organic Chemistry Exam 1

Cyclopentane

________ (108, only slight angle strain, exhibits some torsional strain, envelope form relieves some torsional strain)

Cyclopropane

________ (60, severe angle strain that can be alleviated by orbitals bending but this increases energy due to inefficient overlap of orbitals.

Alkyl Halide

Alkene

Alkyne

Alcohol

Ether

Thiol

Sulfide

Arene

Ketone

Aldehyde

Carboxylic Acid

Acyl Halide

Anhydride

Ester

Amide

Amine

Valence Bond Theory

A covalent bond is formed from the overlap of atomic orbitals. It is also the sharing of electron density.

Atomic Orbital Theory

Overlap of electron cloud

Molecular Orbital Theory

Linear combination of atomic orbitals. Molecular Orbitals are associated with an entire molecule. Treats bonding electrons as being part of the entire molecule.

Antibonding Molecular orbital

Destructive interference, higher energy orbital

Bonding Molecular Orbital

Constructive Interference, lower energy orbital

Hybridization
Steric Number: 2, 3, 4

4-109.5, sp3, 1 sigma bond 3 pi bonds
3-120, sp2, 1 sigma bond 2 pi bonds
2-18-, sp, 1 sigma bond 1 pi bond

Hybridization

Specific orbitals available for bonding

Bond Strength versus Length

Strongest to Weakest: triple, double, and single
Longest to Shortest: single, double, and triple

Sigma Bonds

Head to head over lap of s orbitals

Pi Bonds

Side to Side overlap of p orbitals. They prevent bond axis from rotating, meaning double bonded carbons have no isomers involving rotation. Triple bonds also cannot rotate but it doesn't matter because of their linear geometry.

Molecular Formula

No structure info, just lists the molecule number and their amount

Lewis Structure

Draw all bonds

Partially Condensed Structure

C-H bonds are not explicitly drawn, all other bonds and lone pairs are drawn

Condensed Structure

Single bonds are not drawn. Groups of atoms are clustered together.

Heteroatoms

Atoms other than carbon and oxygen

Formal Charge

Number of valence electrons - (bonds + number of lone pairs)

Hydrocarbon

Contains only C and H

Alkyl Group

Straight branch chain of C and H atoms

R
x
Z

R : Rest of molecule
X : Represents common halogen
Z Represents any group of atoms

Wedge
Dash
Curvy Line

Wedge : Represents a group coming out of the page
Dash : Represents a group going behind the page
Curvy Line : 50% behind and 5-% in front

Acyclic
Cyclic
Bicyclic

Acyclic : No rings
Cyclic : One ring
Bicyclic : two rings

Parent Chain

Select the longest chain to be the parent chain. If two are the same, choose the on with more substituents.

Naming Substituents

add -yl to parent name for substituent name.

Misconceptions

-Prefixes are not used to alphabetize except for iso
-No formula for calculating possible isomers

Isopropyl

1-methylethyl

Sec-butyl

1-methylpropyl

isobutyl

2-methylpropyl

tert-butyl

1,1-Dimethylethyl

isopentyl or isoamyl

3-methylbutyl

neopentyl

2,2 - dimethylpropyl

Assembling Names

-Number all carbon atoms
-First substituent receives lower number, with a tie, the 2nd should be as low as possible
-Further tie, assign alphabetically

Naming Bicyclic

Bicycloalkane : two rings connected to one another
Identify two bridgeheads
Start numbering from bridgeheads, longest to shortest

Constitutional Isomers

Must use all atoms, both structures must be real, must be different compounds. To check if you drew the same isomer twice, use IUPAC naming

Stability of Isomeric Alkanes

Because branched alkanes have a larger heat of combustion their bonds are stronger and more stable

Newman Projections

Achieved due to the rotation about the vertical axis of a c-c single bond

Stereoisomer

Same connectivity but different spatial arrangement

Degenerate

Same amount of energy

Staggered v. Eclipsed

Staggered :
- Possess favorable interactions between an occupied bonding and antibonding sigma orbitals(hyperconjugation)
-60 degree bond angle
-lowest in energy
-Gauche interactions between methyl groups that are right by each other in the conformation (increased energy due to steric interaction)
Eclipsed :
- In the highest energy, the largest molecules are eclipsing each other (steric interaction)
-Experience torsional strain due to the rotation

Cycloalkanes

Ideal angle 109.5. Anything that deviates from that is angle strain. Cyclopropane ( 60, severe angle strain that can be alleviated by orbitals bending but this increases energy due to inefficient overlap of orbitals. Torsional strain due to eclipsed conformation) Cyclobutene ( 90, less angle strain but more torsional bc four sets of eclipsing hydrogens, can adopt a puckered formation without gaining strain ). Cyclopentane ( 108, only slight angle strain, exhibits some torsional strain, envelope form relieves some torsional strain ). Cyclohexane ( 120, nearly strain free. Chair and boat conformation. ). Cycloheptane ( 129 ). Cyclooctane ( 135 ).

Chair

No angle strain, no torsional strain

Half chair

Some angle strain and some torsional strain

Boat

No angle strain, torsional strain and steric strain because of flagpole hydrogens.

Axial v. equatorial

Axial : parallel to vertical axis
Equatorial : along the equator of the ring ( it is favorable to put large groups in equatorial positions because it lowers their potential energy)

Wedge v Dash

Wedge : Up
Dash : Down

Ring flip

Conversion of one chair conformation to the other by rotating all C-C bonds

Cis v trans

Cis : same plane
Trans : opposite plane

Comparing stability

Add up A-Values for axial positions

Haloalkane

Halogen as a substituent

Organohalide

Organic Compound Containing a hydrogen

Stereoisomers

same molecular formula, same connection, different 3D arrangement. Cannot convert one to the other

Superimposable

An object and its mirror image are identical

Chiral object

An object that is not superimposable

Achiral object

An object that is superimposable

A carbon is a chiral center when

It is a tetrahedral bearing four different groups. In a ring it is when the paths around the ring are different

Enantiomer

The non-superimposable mirror image to a chiral compound

Assign priority based on

the atomic number of the substituents, with 1 being the largest priority. If there is a tie, keep moving outwards until something breaks the tie

If priority 4 is on a dash(S and R are what)

R is clockwise and S is counterclockwise

If priority 4 is on a wedge(S and R are what)

R is counterclockwise and S is clockwise

If priority 4 is on plane

Swap 4 with the dashed substituent and then swap the other two

Chiral center on rings

If each side of the carbon is the same (as in there is an internal mirror plane) then it is achiral. If each side is different then it is chiral.

Why is there a dipole moment in trans-1,3-Dichlorocyclobutane?

Cyclobutane adopts a puckered conformation to alleviate torsional strain, causing the dipoles to not fully cancel each other.

Are trans or cis isomers more stable?

Trans isomers. This is because with cis isomers, the bulky atoms are trying to occupy the same space.

Optically Active

A compound is optically active when compounds rotate the plane of polarized light. It is a consequence of chirality

What's the difference in rotation between enantiomers?

Enantiomers will rotate the plane in equal amounts but in opposite directions.

Specific rotation of a molecule is equal to

Observed rotation/(concentration * wavelength)

Enantiomerically Pure

A solution containing a single enantiomer

Racemic mixture

A solution containing equal amounts of both enantiomers, this will be optically inactive

Enantiomeric Excess

Occurs when both enantiomers are contained in unequal amounts

Percent enantiomeric excess equals

rotation of mixture / rotation of pure enantiomer * 100

Enantiomer

Nonsuperimposable mirror image

Diastereomer

Non superimposable not mirror images (Cis trans isomers)

Maximum number of stereoisomers

2^n (n is the number of chiral centers)

Meso compounds

Compounds with a chiral center that are achiral

Presence of a plane of symmetry means

That a compound is achiral and optically inactive

Allenes

Compounds containing two adjacent c=c bonds. Since central carbon is using 2 different p orbitals, it causes a twist, causing chirality

Z v E

If the priority group is on the same side of the double bond, it is Z, if it is the opposite side, it is E.