Chem Final hour 2 - confirmation and configuration

Newman projections stability ranked from greatest to least

Anti staggered > Gauche staggered > Eclipsed > Fully eclipsed with largest groups overlapping

When a molecule’s sigma bond rotates…

it changes its confirmation

staggered confirmation

In the staggered conformation, the substituents of C₁are not aligned with the substituents of C₂. They are not overlapping, they are offset.

Eclipsed Confirmation

the substituents of C₁ are aligned with the substituents of C₂. They overlap. In the eclipsed conformation, the substituents are slightly offset for visualization purposes.

To go from staggered to this specific eclipsed conformation, the sigma bond rotates…

180 degrees

In a newman projection, overlapping is ____ and it produces…

1. unstable

2. torsional strain

Define Torsional strain.

a destabilizing force that is produced by the repulsion between the pairs of electrons of two aligned bonds.

• Produced in Eclipsed molecules

Define Steric Effect.

A destabilizing force that arises from electron clouds from different atoms coming together (bulky groups bumping into each other)

• Produced in staggered confirmations

Anti Staggered

Confirmation in which the largest substituents are separated by 180 degrees

Gauche Staggered

Confirmation in which the largest substituents are separated by 60 degrees

• There is steric effect

Syn-eclipsed

Conformation in which the largest substituents are aligned.

• HIGHEST IN ENERGY

Angular Strain

A destabilizing force that occurs when bonds are pushed closer, forming angles that are smaller than their ideal arrangement angles

• Sp3 hybridized atoms contain bonds with 109.5 angles between them

Having a substituent in the axial conformation produces ___ and ____ strain… meaning that the _____ confirmation reduces steric strain

1. Steric

2. Torsional

3. Equatorial

Cis conformational structure for chairs (on adjacent carbons)

• Both substituents are pointing up (wedge)

• One is axial and the other is equatorial

Trans conformational structure for chairs (on adjacent carbons)

• One substituent is pointing up and the other is down

• Can be a diequatorial structure (more stable)

Trans conformational structure for chairs (not on adjacent carbons)

• One substituent is pointing up but the other is down

• one is axial and the other is equatorial

cis ring conformation

Both is equitorial

Cis ring conformation (pt 2)

1 equitorizl

1 axial

Trans ring conformation

Trans ring conformation

Constitutional Configuration

Same number and types of atoms, but different connectivity

Conformational Configuration

Different 3D arrangement of the same molecule as a results of bond rotation (like staggered and eclipsed)

Configurational Configuration

Same connectivity, but different 3D arrangement that cannot be changed by rotation (like trans and cis, or S and R, which are covered in this lecture)

Enantiomers

Two non-identical mirror images

• not interconvertible by rotation

Differences between Enantiomers and disastereomers

Enantiomers - identical mirror images of each other

disastereomers - a change in configuration (but not mirror imaged)

How to determine if a solution is optically active

• Has only 1 enantiomer

• unequal mixture (not 50%)

• is Trans on non-adjacent Carbons

Compounds that might be separated by chromatography when using a achiral stationary phaseEnantiomers —→ Not separated

• Enantiomers —→ Not separated

• Different molecules & Diastereomers —→ will be separated

Other Diastereomers…

• if a molecule changes from E to Z

• if 2 molecules change positions