o-chem lab 8

equation for ee given percents of two enatiomers

% of one enantiomer- % of the other enantiomer= ee

what enantiomer of tartaric acid do we use?

(+)-tartaric acid

which is less soluble salt of alpha-methylbenzlamine + or -

(-) alpha-methylbenzlamine

1dm = ____ cm

10

for a molecule with n stereogenic centers, the maximum number of stereoisomers is ___

2^n

A particular ____ is called a configuration

3D arrangement

if a mixture contains 75% of one enantiomer and 25% of the other, the enantiomer excess is ____

50%

how does optical rotation of enantiomer A, B and racemic mixture differ

A=(-)B; A+B=0

how does boiling point of enantiomer A, B and racemic mixture differ

A=B but A+B may not be equal to A or B

how does melting point of enantiomer A, B and racemic mixture differ

A=B but A+B may not equal A or B

When a compound has more than one stereogenic center ___ and ___ configurations must be assigned to them

R; S

Since enantiomers are two different compounds they need to be distinguished by name. This is done by adding ___ or ____ to the IUPAC name of the enantiomer

R;S

label following priorities T D H

T=1=tritium=mass number of 3 (1 proton + 2 neutrons) D=2=deutereum=mass number of 2 (1 proton 1 neutron) H=3=hydrogemass number of 1 (1 proton)

____ usually contain a plane of symmetry but ___ don't

achiral; chiral

In this lab you will be using diastereomeric salt formation between a racemic mixture of ____ and _____

alpha methylbenzylamine; tartaric acid

equation for specific rotation

alpha=observed rotation l= length of sample tube (dm) c=concentration in grams/mL

with one stereogenic center a molecule will ___ be chiral. With two or more ___

always; it may or may not be chiral

If a molecule and its mirror image are not superimposable the molecule and its mirror image are ___

chiral

Naturally occuring tartaric acid is ___

chiral

a ____ compound is non-superimposable on their mirror-images

chiral

a ____ object cannot be superimposed on its mirror image

chiral object

The chemical and physical properties of two enantiomers are identical except in their interactions with _____

chiral substances

Many drugs are ___ and often must react with a ____. This means that one enantiomer of a drug may effectively treat a disease whereas the mirror image may be ineffective or toxic

chiral; chiral receptor or chiral enzyme

The rotation of polarized light can be ____ or ___

clockwise or anticlockwise

a particular 3D arrangement is called ___

configuration

2 types isomers

constitutional isomer; stereoisomer

_____ are isomers having atoms bonded to different atoms

constitutional isomers

If the rotation is clockwise the compound is called _____. The rotation is labeled ___ or ___

dextrorotatory; d; +

In this la you will be using _____ formation between a _____ of alpha methylbenzylamine and tartaric acid (ionic interactions)

diastereomeric salt formation; racemic mixture

_____ are stereoisomers that are not mirror images

diastereomers

_____ are stereoisomers which are not even mirror images of one another

diastereomers

____ and ____ have different physical properties, and therefore can be separated by _____

diastereomers; constitutional isomers; common physical techniques

to find the other two stereoisomers if they exists ___ and determine ____

draw the mirror images of each compound; determine whether the compound and its mirror image are superimposable

equation for enantiomeric excess using specific rotation

ee=[specific rotation of mixture/specific rotation of pure enantiomer] x 100%

optical purity is another name for _____

enantiomeric excess

what does ee stand for

enantiomeric excess

____ are stereoisomers that are mirror images

enantiomers

_____ are stereiosomers which are mirror images of one another

enantiomers

levotartaric and dextrotartic acid are ____

enantiomers

____ have identical physical properties, they cannot be separated by ___ like ___

enantiomers; common physical techniques ; distillation

two types of stereoisomer

enantiomers; diastereomers

_____ is a measurement of how much one enatiomer is present in excess of the racemic mixture

enatiomeric excess

an _____ is called a racemic mixture or racemate

equal amount of two enantiomers

two enantiomers rotate plane polarized light to ____ but in ___

equal extent; opposite direction

when extracting less soluble salt we get isolation of ____- ___ by the addition of a ____

free amine; deprotonaition; aqueous NaOH

How could you use column chromatography to separate two enantiomers

if there was a chiral column packaging/stationary phase. two different enantiomers interact differently with it and one goes through faster

The physical properties of enantiomers are identical excpet in how they ____

interact with plane-polarized light

_____ are different compounds with the same molecular formula

isomer

What does the D/L mean in D-(-)-tartaric acid and L-(+)-tartaric acid mean

it refers to the orientation of optica rotation (+ for dextrorotary, - for levotarty)

If the rotation of plane polarized light is counterclocwise the compound is called ____. The rotation is labeled ___ or ___

levorotatory; l; -

a ____ is an achiral compound that contains 2 or more tetrahedral stereogenic centers

meso compound

_____ is a diastereomer of levotartaric and dextrotaric acids

mesotartaric

_____ exists between R and S prefixes and + and - designations that indicate optical rotation

no relationship exists

a chiral compound is ___

not superimposable on their mirror images

The angle alpha is measured in degrees (^o) and this is called the ____. A compound that rotates polarized light is said to be _____

observed rotation; optically active

if o.p. is 50 then the observed rotation would be ___

only 50% of the rotation of the pure enantiomer (mixture composition=75-25)

____ is also called enantiomer excess

optical purity

____ is another name for enantiomeric excess

optical purity

A compound that does not change the plane polarized light is said to be ____

optically inactive

A racemic mixture is ____ because the two enatiomres ___

optically inactive; rotate plane-polarized light to an equal extent but in opposite directions, the rotations cancel and no rotation is observed

plane-polarized light arises from ____

passing light through a polarizer

achiral molecules usually contain a _____ but chiral don't

plane of symmetry

meso compounds generally contain a ____ so that they possess ___

plane of symmetry; two identical halves

_____ is light that has an electric vector that oscillates in a single plane

plane-polarized (polarized) light

______ arises from passing ordinary light through a polarizer

plane-polarized light

a ____ is an instrument that allows polarized light to travel through a sample tube containing an organic compound

polarimeter

a polarimeter is an instrument that allows _____ to travel through a ____. It permits the measurement of the degree to which an organic compound ____

polarized light; sample tube containing an organic compound; rotates plane-polarized light

optical purity is the amount of _____

pure enantiomer in excess of the racemic mixture

we separate enantiomers: we react a ___ with a _____ to form _____ which can be separated

racemic mixture; chiral compound; diastereomers

an equal amount of two enantiomers is called a ____ or ___

racemic mixture; racemate

how to extract less soluble salt from methanol

react with ether

With achiral compound the light in the polarimeter exiting the sample tube ___

remains unchanged

Many biologically active molecules contain stereogenic centers at ____

ring carbons

With chiral compound the plane of polarized light is ____

rotated through an angle alpha

____ is a standardized physical constant for the amount that a chiral compound rotates plane-polarized light

specific rotation

_____ are isomers with a difference in 3-D arrangemetn only

stereiosomers

many biologically active molecules contain _____ centers at ring carbons

stereogenic centers

____ differ in configuration

stereoisomers

_____ are molecules which have the same bonding sequence but different arrangements in space

stereoisomers

What happens to the tartaric acid

tartaric acid reacts with base... proton transfer to the NH2 on the base... causes an ionic attraction between CB of tartaric acid and CA of alpha-methylbenzlamine. Causes it to dissolve. One entianomer dissolves ore than other in aqueous. Take less aqueous crystals. React with NaOH to get aqueous back. Distillation under reduced pressure.

a carbon atom with four different groups is a ____

tetrahedral stereogenic center

observed rotation depends on ____, ____ , ____, ___ and ___

the length of the cell; concentration; optical activity; temperature; wavelength of light

Two enantiomers have exactly the same chemical properties except for ___

their reaction with chiral non-racemic reagents

when assigning priorities. the C of a C=O is considered ___

to be bonded to two O atoms

How to we separate enantiomers

we react a racemic mixture with a chiral compound to form diastereomers which can be separated