orgo lab final

general theory of IR

The general theory of infrared spectroscopy explains how molecules absorb infrared light at specific frequencies based on their vibrational transitions; they bend and stretch

symmetric stretch:

asymmetric stretch:

bending:

symmetric=both sides same direction

asymmetric=one side stretch

bend=in and out o plane

spectroscopy

study of electromagnetic radiation (light)

wavelength and frequency:

Ephoton and frequency:

wavelength and frequency=indirectly proportional

Ephoton and frequency=directly proportional

the frequency at which a peak appears on an IR spectrum

is the result of the IR absorption of specific wavelengths of light by molecular vibrations.

a strong IR absorbance

percent transmittance is near 0; bottom of spectrum

a weak absorbance

percent transmittance is near 100; top of spectrum

bonds in IR spectrum

a given type of bond will have the same absorption frequency of IR among different molecules; does not change among molecules

(C,N,O)-H stretches

between ~2500 and 400

triple bonds

between 200 and 2500

double bonds

~1500 and 2000

single bonds

between ~1000 and 1500

finger print region

below ~1400

functional group region

above 1400

hooks law

when you have a large atom and a small atom you will have a higher vibrational frequency

the more polarized a bond

the more intense of a peak

alkane C-H

below 3000

alkene C-H

between ~3000 and 3100

alkyne C-H

at ~3300

length of bonds longest to shortest (directly proportional to strength)

sp3→sp2→sp

carbonyl stretch

1700

OH stretch

intense and broad, centered above 3000 (smooth curve)

carboxylic acid stretch

centered above 3000 and can extend to 2500 (more broad than alcohol and bumpy)

frequency of bonds (more frequent to less frequent)

single→double→triple bonds

IR absorption and dipoles

directly proportional

goal of simple distillation

purify one liquid from a mixture

predicting concentration of vapor

when you boil a mixture, the vapor will be more concentrated in the substance that has more pressure.

distillation theory

a liquid and its vapor exist in equilibrium

less vap at equilibrium (low vap pressure)=

more vap at equilibrium (higher vap pressure)=

less vapor =less volatile

more vapor=more volatile

miscible liquids

homogeneous solution (will not separate)

purpose of distillation in lab

separate and isolate a desired liquid component

which substance distills first

more volatile liquid will distill first

general distillation rule

1. a mixture of liquids will boil when the total pressure over the mixture equals the external pressure

2. the vapor will be different than the liquid (richer in the more volatile component; higher Pvap)

3. if that vapor is condensed the liquid will have the same composure (richer in the more volatile component)

distillation

the process of vaporizing a liquid mixture in one vessel and condensing the vapors into another

distilland

the liquid mixture being distilled

distillate

recondensed vapors resulting in the liquid

result of distillation

more volatile component will end in receiver flask and less volatile component will remain in pot

volatillity

the tendency for a liquid to vaporize

boiling point and Pvap

temp at which the vapor pressure of the liquid is the same as the atmospheric pressure

thus, the mixtures boiling point will be between the two boiling points of the pure liquids

daltons law

total gas pressure of mixture is determined by adding the individual pressures of each liquid together.

raoults law

is the vapor pressure of one liquid component in a mixture.

(vapor pressure of pure liquid) x (mole fraction of liquid component in mixture)

mole fractions

# of moles of the liquid component/total # of moles of each component in liquid mixture

boiling point

temp at which a pure organic substance is changed from the liquid phase to the gas phase

bubble point temp

when liquid is nearing boiling point some molecules go from the liquid phase to the gas phase (bubble point is same as boiling point in pure liquid)

dew point temp

temp at which the first liquid drops begin to form during distillation

vapor-liquid equilibrium diagram (top and bottom curve)

shows the change of the liquid composition in the flask and the distillate over the distillation.

bottom curve=the boiling point of the liquid in the flask

top curve=the temp of the vapor as it relates to its composition

melting point

temp at which a solid melts (intermolecular forces are overcome)

binary solid

a mixture of two compounds that are blended together really closely at the molecular level

intermolecular forces trend

when a substance is impure the intermolecular bonds are weaker due to the foreign substance so he melting point is lower; because it takes less energy to break the bonds because they are weaker

how we use melting point in recrystallization

used to determine the purity of a crystalline solid and tell us information about the stability of the formed crystals

crystalline solids

form a lattice. requires thermal energy to break.

impurities

effect melting points. adding impurities decrease melting points.

make pure solid weaker because the intermolecular forces are weaker. Takes less energy (heat) to break the bonds.

melting point important

gives information about the identity and purity as well as the bonding strength within the crystal lattice

rapid cooling

causes impurities to get stuck in the crystal lattice

recrystallization theory

solubility→extent of dissolving solute in solvent

solubility rules

1. like-dissolves-like

2. solubility increase with temp increase

recrystallization in practice

remove impurities from desired solid

solvent requirements: solid must be soluble in solvent when temp increases and insoluble when temp decreases. Impurities must always be soluble in solvent.

cooling: must be slow

% recovery

mass of result solid/mass of crude solid

melting point analysis

melting point range: when melting starts → completely melted

narrower range +close to lit. MP=more pure

broader range + lower than lit. MP= less pure

incongruent melting

a compound now melts at a range of temperatures rather than a single fixed temp. when melting a mixture one component enters the liquid phase quicker than the other.

eutectic point

single and lowest temp of melting of of any mixture of the two components

liquid-liquid extraction laws

1. liquids which do not dissolve in one another are called immiscible

2. immiscible liquids form two distinct phases when mixed

3. solute molecules can partition between two phases

high polarity solute

favors aqueous phase (small partitioning coefficient=small#/large#)

low polarity solute

favors organic phase (large partitioning coefficient= large#/small#)

organic liquid

liquid that is not water

charged and uncharged components

uncharged: usually water insol. (organic sol.)

charged: usually water sol. (organic insol.)

liquid-liquid extraction purpose

to isolate a target liquid from a mixture or to separate two immiscible liquids

Ionic salts

more soluble in water less soluble in organic liquid