Organic Chem Exam 2 Terms

What does it need to contain to be an aromatic compound?

A planar, flat cyclic conjugated pi system, which follows Huckel's rule of having a total of (4n + 2) pi electrons.

Conjugated

systems are alternating single and double bonds that allow for delocalization of pi electrons (all atoms have a p orbital)

What is the difference between aliphatic compounds and aromatic rings?

Aliphatic compounds feature straight chains, branched chains, or non-aromatic rings with single, double, or triple bonds, whereas aromatic compounds contain a planar, cyclic ring with a delocalized pi-electron system that follows Hückel's rule

Bromobenzene

An aromatic compound consisting of a benzene ring with a bromine substituent.

Nitrobenzene

An aromatic compound containing a benzene ring with a nitro group (NO2) as a substituent.

Propylbenzene

An aromatic compound containing a benzene ring with a propyl group (CH2CH2CH3) as a substituent.

Toulene

An aromatic hydrocarbon consisting of a benzene ring with a methyl group (CH3) as a substituent.

Aniline

An aromatic amine consisting of a benzene ring with an amino group (NH2) as a substituent.

Phenol

An aromatic compound consisting of a benzene ring with a hydroxyl group (OH) as a substituent.

Styrene

An aromatic compound consisting of a benzene ring with a vinyl group (C=C) as a substituent.

Xylene

An aromatic hydrocarbon consisting of a benzene ring with two methyl groups as substituents.

Ortho position

The ortho position refers to the location of two substituents on a benzene ring that are adjacent to each other, specifically at the 1,2-positions.

Meta position

The meta position refers to the location of two substituents on a benzene ring that are separated by one carbon atom, specifically at the 1,3-positions.

Para position

The para position refers to the location of two substituents on a benzene ring that are opposite each other, specifically at the 1,4-positions.

What is electrophilic aromatic substitution (EAS)?

Electrophilic aromatic substitution (EAS) is a chemical reaction in which an electrophile reacts with an aromatic ring, replacing one of the hydrogen atoms on the ring.

What is the generic mechanism for EAS?

The e- reach out and grab e+, then the e- in C-H bond shift into the ring to re-establish aromaticity.

Benzenes pi electrons participate as:

A lewis base in reactions with lewis acids

Enantiomers

Molecules that are not the same as their mirror image

They are enantiomers if:

The positions of the atoms can coincide on a one-to-one basis when one is a non-superimposable mirror image of the other.

What does superimposable mean?

It means that two molecules can be placed on top of each other and coincide in all aspects, indicating they are identical.

What does non-superimposable mean?

It refers to two molecules that cannot be perfectly aligned or placed on top of each other, meaning they are distinct and not identical.

What is a chirality center?

A carbon atom that is bonded to four different substituents, resulting in non-superimposable mirror images.

Molecules that are not superimposable with their mirror images are:

Chiral

Chiral means:

a property of a molecule that is not superimposable on its mirror image, “have handedness”

What is a plane of symmetry?

Divides an entire molecule into two pieces that are exact mirror imagesof each other, indicating achirality.

What does it mean if a molecule is achiral?

It means that the molecule is superimposable on its mirror image, indicating a lack of handedness, where it can be divided into two identical halves.

The lack of a plane of symmetry is called:

Handedness, also known as chirality, indicates that a molecule has distinct non-superimposable mirror images.

Examples of chirality?

Hands, gloves, cork screws (their divots make it to where they can only twist one correct way)

Examples of achirality?

Basketball, wine glass, snowflake

A point in a molecule where four different groups (or atoms) are attached to a carbon is called:

A chirality center

Groups attached to a carbon are considered “different” if:

There is any structural variation (if the groups could not be superimposed if detached, they are different)

In cyclic molecules, how do we determine chirality?

We compare by following each direction around the ring to see if the groups result in a mirror image.

Light restricted to pass through a plane is called:

plane-polarized light

Plane polarized light that passes through____retains its original plane polarization

Solutions of achiral compounds

Solutions of chiral compounds rotate plane-polarized light and the molecules are said to be:

Optically active

Clockwise rotation is called:

Dextrorotatory, R

Counter clockwise is called:

Levorotatory, S

What does a polarimeter do?

Measures the rotation of plane-polarized light that has passed through a solution

In a polarimeter, the angle between the entrance and the exit planes is:

The optical rotation

Recalling the Cahn-Ingold-Prelog rules, recall the steps.

1.) Identify the four substituents attached to the chiral center.

2.) Assign priority based on atomic number. (1 is the highest, 4 is the lowest, and remember first point of difference rule!)

3.) Orient the molecule so the lowest priority group is pointing away from you.

4.) Determine the order of the remaining groups to establish the configuration as R or S.

What is the first point of difference rule? (AKA tie-breaker)

When two substituents have the same atomic number, compare the atomic numbers of the atoms attached to them until a difference is found, using the first differing atom to determine priority.

What is a diastereomer?

A stereoisomer that is not a mirror image of another. Diastereomers have different physical properties and are not superimposable.

WHat is a stereoisomer?

A compound that has the same molecular formula and connectivity of atoms but differs in the arrangement of its atoms in space. Stereoisomers include both enantiomers and diastereomers.

What is a meso compound?

A compound that has multiple chiral centers but is superimposable on its mirror image due to an internal plane of symmetry.

What is a racemic mixture?

A 50:50 mixture of two chiral compounds that are mirror images that do not rotate light (optically inactive)

What is a racemate?

A specific type of racemic mixture consisting of equal amounts of both enantiomers of a chiral molecule.

WHat is the difference between a constitutional isomer and a stereoisomer?

Constitutional isomers differ in connectivity of atoms, while stereoisomers have the same connectivity but differ in spatial arrangement (enantiomers and diastereomers).