OChem 1 lab exam

5 steps of recrystallization

1. choose an appropriate solvent

2. dissolve impure mixture in the hot solvent

3. remove the insoluble impurities from the hot solvent

4. cool filtrered solution, crystalize the solid

5. isolate the impure compound

to induce crystallization

1. strach the inner wall with a stirring rod

2. introduce seed crystal

3. boil off some solvent and re-cool

what happens to melting point when there are impurities

impurities will broaden and supress our melting point

Eutectic point

an impure mixture of compounds A and B will melt will melt at a point which is lower than the individual melting points of A and B

Distillation

Liquid vaporizations followed by condensations

two types of distillation

simple and fractional

simple distillation

boiling point difference of 100 C or greater

Fractional distillation

boiling point difference less than 100 C

why do fractionating columns help in fractional distillation

it uses back to back mini simple distillations

Theoretical plates

represents the overall efficiency of the fractionating column (more plates = more efficient)

Azeotrope

two miscible liquids behve as a pure liquid (one boiling point)

Raoults law

Pt = (Xa)(Pa) + (Xb)(Pb)

Mole fraction

Xa (part/whole)

with less atospheric pressure what happens to altitude and boiling point

decrease atmospheric pressure, increase altitude, decrease boiling point

Extraction

a single component is removed from a mixture of others

solid liquid extraction

component seperation based on compounds solubility in a particular solvent system

liquid liquid extraction

component seperation based on a compound’s varying solubility between two immisicle liquid phases

miscible

capable of mixing

immiscible

incapable of mixing

starting material and product of solid liquid extraction of nutmeg

starting material: Nutmeg

product: Trimyristin

goal of thin layer chromatography

multicomponent mixture identification

TLC plate stationary phase

silica gel (polar)

TLC plate mobile phase

ehtyl acetate containing 0.5% acetic acid (nonpolar)

retention factor

how far each compound migrated from the baseline, used to identify the compounds

retention factor math

distance from origin to sample/distance from origin to solvent front

relationship between polarity and Rf

as retention factor increases, polarity decreases

acid/base liquid extraction

move compounds between immiscible aqueous and organic layers

Heavier densiity layer is on

bottom

aqueous layer is

water

organic layer is either

dichloromethan or ethyl acetate

if organic layer is ethyl acetate it will be

on top

if organic layer is dichloromethane it will be

bottom layer

acid react with ___ to become charged

based

base react with ___ to become charged

acid

what is the reagent for transfer hydrogenation of olive oil

cyclohexane (hydrogen donor)

realtionships between cyclohexane and double bonds

1 cyclohexane: 2 double bonds

preparation of diphenyl acetylene

involves halogenation of an alkene followed by dehydeogenation of the alkyl halide resulting in the formation of a triple bond

PHPB

pyridinium hydrobromide perbromide

reflux

heat to a really high temperature without losing solvent

what is Gas Chromatography

determines ratio of product formation

mobile phase for gas chromatography

inert gas (flow rate of gas)

stationary phase for gas chromatography

nonvolatile liquid coated on column

4 ways to adjust the way a compound sepretes in a in GC

1. change the temp

2. change the stationary phase

3. change the column length

4. change the mobile phase

nucleophile strength in aprotic

stronger the base, better the nucleophile

nucleophile strength in protic

stronger base = best nucleophile unless in same column, then bigger is better

SN2 subsitution preference

1 > 2 > > > 3

catalysts for williamson ether synthesis

potassium hydroxide and terta-N-butylammonium bromide

base catalysts for williamson ether synthesis

KOH

TBAB

terta-N-butylammonium bromide - phase transfer catalyst that works by helping ions cross between the organic and aqueous layer

How is GC and TLC similar

GC like TLC becuase components of a mixture are seperated based on affinity for mobile phase and stationary phase