ORGCHEM LEC: ISOMERS

What are the 2 types of isomers depending on CONNECTIVITY?

1. -

2. -

Constitutional isomer
Stereoisomer

____________ are isomers with DIFFERENT connectivity

Constitutional isomers

What are the 3 types of CONSTITUTIONAL isomers?

1. -

2. -

3. -

Skeletal
Functional
Positional

_____________ are constitutional isomers that are different in BRANCHING/PARENT LENGTH

Skeletal

______________ are constitutional isomers that are different in FUNCTIONAL GROUPS

Functional

_____________ are constitutional isomers that are different in POSITION/LOCANT

Positional

__________________ are isomers with the SAME CONNECTIVITY but with DIFFERENT ARRANGEMENT

Stereoisomers

___________________ have the SAME CONNECTIVITY but differ in 3D ARRANGEMENT

Stereoisomers

What are 2 types of STEREOISOMER?

1. -

2. -

Configurational
Conformational

__________________ are stereoisomers with TEMPORARY differences due to the free rotation of SIGMA BONDS. These can freely rotate in space and doesn’t have much strain since SINGLE BOND.

Conformational

CONFORMATIONAL are stereoisomers with __________ differences due to the free rotation of ______________. These ______ freely rotate in space and doesn’t have much strain since _______________.

temporary
sigma bonds
can
single bond

___________ allow free rotation

single bonds

In CONFORMATIONAL. the bond rotation ____ interchange isomers

can

_________________ are stereoisomers with PERMANENT differences. These CANNOT be interconverted freely due to RIGIDITY.

To be interconverted, there should be BREAKING OF BONDS through chemical reactions.

These are common in RINGS and DOUBLE BONDS (sp2)

Configurational

CONFIGURATIONAL are stereoisomers with ___________ differences. These _______ be interconverted freely due to _________.

To be interconverted, there should be _______________ through _______________.

These are common in ________ and _______________ (sp2)

permanents
cannot
rigidity
breaking of bonds
chemical reactions
rings
double bonds

In the _____________ conformation, the substituents are attached to carbon 2 and the opposite/substituents are FAR from one another

staggered

In the _____________ conformation, the C-H bonds on the front and back are aligned

Eclipsed

When the distance between bonds and atoms INCREASE, the compound’s stability ____________

INCREASES

________________ are a type of CONFORMER that can ROTATE FREELY and INFINITELY

Rotamers

The _________________ of cyclohexane DOES NOT give TORSIONAL STRAIN since hydrogens have enough distance between them

Chair conformer

The ________________ of cyclohexane GIVES TORSIONAL STRAIN as the hydrogens have small distances between them

Boat conformer

Conformational — Stability
Staggered: ________
Eclipsed:__________
Chair: ____________
Boat: ____________

High
Low
High
Low

What are the 4 conformations of butane in Newman projections?

1. -

2. -

3. -

4. -

Anti
Gauche
Eclipsed
Syn

Stability of Butane based on Newman projection (ARRANGE STARTING FROM MOST STABLE TO LEAST STABLE)

Gauche (60 degrees)
Eclipsed (240 degrees)
Anti (180 degrees)
Syn (0 degrees)

Anti > Gauche > Eclipsed > Syn

_______________: These 6 bonds, one on each carbon, are PARALLEL and alternate UP-DOWN

Axial bonds

_____________: These 6 bonds, one on each carbon, come in 3 sets of 2 PARALLEL lines. Each set is also parallel to two ring bonds. These alternate between SIDES around the ring

Equatorial bonds

________________ is the stereoisomerism that is NOT INTERCONVERTIBLE by rotation around a bond

Geometric isomers

______________ are also known as “cis-trans” isomers

Geometric isomers

_______________ is the configuration determined by RESTRICTION OF BOND MOVEMENT by either RINGS(sp3) or DOUBLE BONDS(sp2)

Geometric isomers

_______ are similar substituents on the SAME side

Cis

__________ are similar substituents on the OPPOSITE side

Trans

Cis or trans prefixed can ONLY be used if each sp2 carbon has only ______ substituent (not zero, not two)

Not zero, puro hydrogens
Not two, different substituents

ONE

For double bonds with any sp2 carbon having 2 substituents, use the ___ or ____ descriptors instead.

E
Z

Whether it’s E or Z will be based on the _____________________

Cahn-Ingold-Prelog rules

The prioritization in E/Z and optical isomers is based on the _______________ of the FIRST ATTACHED ATOM

atomic number

Atomic number ranking

1. -

2. -

3. -

4. -

5. -

6. -

7. -

8. -

9. -

Bromine
Chlorine
Sulfur
Phosphorus
Oxygen
Nitrogen
Carbon
2 Hydrogen
1 Hydrogen

In the Cahn-Ingold-Prelog rules, if the first attached atoms are the same, compare all ____________ atoms next

adjacent

What are the 2 types of isomers under CONFIGURATIONAL?

1. -

2. -

Optical
Geometric

____________________ are NONSUPERIMPOSABLE or CANNOT perfectly align. This configuration is determined by ASYMMETRY.

Optical isomers

When asymmetry is present, then it is ________________

Nonsuperimposable

When it is asymmetrical, then it is ____________________ or capable to rotate the plane polarized light through the use of POLARIMETER.

Optically active

___________________ is when the carbon atom has 4 DIFFERENT substituents (sp3 hybridization)

Chirality

_____________ when there is any form of symmetry present, therefore NOT optically active

Achiral

Chiral carbon is also called as ______________ or ____________

chiral center
stereogenic center

Asymmetric compounds have ______________

optical activity

In using the polarimeter, there is

_____________ = CLOCKWISE (+)

_____________ = COUNTER CLOCKWISE (-)

Dextrorotatory
Levorotatory

CIP Rules for OPTICAL ISOMERS

___________ when it is turned CLOCKWISE

___________ when it is turned COUNTER CLOCKWISE

Rectus
Sinister

Whether a compound is assigned R or S ____________ equate to their dextro- or levo- spin

DOES NOT

What are the 2 types of isomers under OPTICAL ISOMERS?

1. -

2. -

Enantiomers
Diastereomers

_______________ are NONSUPERIMPOSIBLE. These are MIRROR-IMAGES in which ALL CHIRAL CARBONS are INVERTED. 

Enantiomers

One molecule can only have _____ enantiomer of itself

One

___________________ or __________ is a combination of the enantiomers which are OPTICALLY INACTIVE because they cancel out

Racemic mixture
Racemate

________________ is the separation of a racemic mixture to make them diastereomers

Resolution

___________________ are NONENANTIOMERS. These are NOT real mirror images since only SOME chiral carbons are inverted

Diastereomers

______________ have 2 chiral carbons that are MIRRORS of each other thus CANCELLING EACH OTHER OUT. They become SYMMETRICAL which means they are OPTICALLY INACTIVE

Meso compounds

_____________ are INTERCONVERTIBLE by rotation about single bonds

Conformers

______________ are NOT interconvertible by rotation, only by BREAKING and MAKING bonds

Configurational

_______________ are MIRROR IMAGE, NOT SUPERIMPOSABLE on itself

Chiral

___________: molecule and mirror image are IDENTICAL

Achiral

_______________: MIRROR IMAGES, have OPPOSITE configurations at ALL stereogenic centers

Enantiomers

_________________: stereoisomers but NOT MIRROR IMAGES, have SAME configuration at one or more centers, but DIFFER at the remaining stereogenic centers

Diastereomers