ISOMERS

isomers

Are compounds having the same numbers

and kinds of atoms but differ in the way

the atoms are arranged.

structural (constitutional) isomers

stereoisomers

what are the types of isomers

constitutional isomer

what type of isomer that has a different bond pattern

stereoisomers

what type of isomer has the same pattern

skeletl

functional

positional

what are the three types of constitutional isomer

Stereochemistry

the branch of chemistry concerned with the

three-dimensional structures of molecules.

Stereoisomers

Same molecular formula and constitution but

different spatial (3D) arrangement of atoms

Stereoisomers

same connectivity

conformers, rotamers

Different arrangement due to rotation

around a SINGLE BOND (mula sa single bond, pwedeng umikot)

Staggered (99%)

The lowest-energy, most stable

conformation

Staggered (99%)

all six C–H bonds are as far away

from one another as possible

Eclipsed (1%)

The highest-energy, least stable

conformation

Eclipsed (1%)

six C–H bonds are as close as

possible

anti

methyl groups are farthest apart

gauche

methyl groups experience a _______ interaction. (nagbabanggaan)

STERIC STRAIN

REPULSION AS A RESULT OF

TRYING TO OCCUPY THE SAME SPACE

Geometric (Cis-Trans) Isomers

Lack of rotation in C=C bonds

• For disubstituted alkenes

cannot

When two identical groups are connected to

the same position, there cannot/ can be cis-trans

isomerism.

strong acid catalyst

the interconversion of cis and trans

alkene isomers doesn’t occur spontaneously, it

can be brought about by treating the alkene with

a ______________.

stereochemistry

Chemistry concerned with 3D structures

• Focus on chirality (ky-ral-i-tee), or handedness

(Greek cheir, meaning “hand”)

Chirality

Any object can be viewed in a mirror, revealing

its mirror image.

SUPERIMPOSABLE

The mirror image is identical to the actual object.

NONSUPERIMPOSABLE

The object and its mirror image are different.

stereocenter, or chirality center

The presence of a carbon atom bonded to

four different groups

Plane of symmetry

a plane that cuts through the middle of a

molecule or other object so that one half of

the object is a mirror image of the other

half.

achiral

what do you call a molecule that contains a plane of symmetry. (not chiral)

optical activity

Ability to rotate a beam of plane-polarized

light

Polarimeter

Measures the amount of rotation

Dextrorotatory (+)

Some optically active molecules rotate plane-

polarized light

– to the right (clockwise)

Levorotatory (-)

Some optically active molecules rotate plane-

polarized light

to the left (counterclockwise)

active, rotate

chiral compounds are optically _______ and ______ polarized light.

inactive, do not

achiral compounds are optically _______ and ______ polarized light.

Racemetes

A.k.a. racemic (rah-see-mic) mixtures

• 50:50 mixture of enantiomers

Enantiomers

Stereoisomers that are

nonsuperimposable mirror image

Diastereomers

Stereoisomers that are NOT mirror images

of each other

Meso Compounds

Compounds that are achiral, yet contain

stereocenters

chiral

only _____ compounds have enantiomers

Chirality

Objects that are not superimposable on their

mirror images are called chiral objects.

CHIRALITY CENTER

The most common source of molecular chirality is the presence

of a carbon atom bearing four different groups.

Chiral center, stereocenter, stereogenic center, asymmetric center, CHIRAL CARBON

enantiomer

When a compound is chiral, it will have one

nonsuperimposable mirror image, called its ____________ (from the Greek word meaning

“opposite”)

R configuration (Latin rectus, meaning “right”)

Priority substituent (1 - 2- 3) is clockwise,

S configuration (Latin sinister, meaninng right

If an arrow from 1 - 2 - 3 is counterclockwise,

fluoxetine

a commonly prescribed medication

sold under the trade name Prozac.

racemic fluoxetine

is an extraordinarily effective

antidepressant, but it has no activity against

migraine.

The pure S enantiomer

works

remarkably well in preventing migraine and is

now undergoing clinical evaluation.

To exert its biological action, a chiral molecule

must fit into a chiral receptor at a target site

Why do different stereoisomers have different

biological properties?

oranges

the (+)

enantiomer of limonene has the odor of ________

piney scent.

the

(−) enantiomer has a ___________

chiral diastereomers

multiple stereocenters

cis-trans diastereomers

double bond or ring