how are organic compounds analysed and used?

testing for C=C bonds

• bromine water test

• iodine number

bromine water test

• unsaturated compound + Br₂ → brominated product (addition reaction)

  • orange/brown → colourless

• saturated compound + Br₂ → no reaction

  • orange/brown colour persists

iodine number

m (I₂) reacts with 100g cheical substance

• 1 mol of I₂ = 1 mol of C=C

testing for hydroxyl groups

• sodium metal test

• oxidation test

• esterification test

sodium metal test

• if sample is alcohol, mixing it with Na _(s) will create H_{2 (g)}

• pop test to confirm

oxidation test

• primary alcohol → _{oxidising agent (}Cr₂O₇^2-/H⁺_{) (low temp)} aldehyde → _{oxiding agent (}Cr₂O₇^2-/H⁺_{) (high temp)} carboxylic acid

  • orange → green

• secondary alcohol → _{oxidising agent (}Cr₂O₇^2-/H⁺₎ ketone

  • orange → green

• tertiary alcohol → no reaction

  • orange persists

esterification test

• if fruity smell detected, ester is produced

testing for carboxyl group

• pH test

• metal hydrogen carbonate test

• esterification test

pH test

• acid-base indicators

• carboxylic acids are weak and only partially ionise

• ↑ [H⁺]/[H₃O⁺], ↑ acidity, ↓ pH

metal hydrogen carbonate test

• if sample is a carboxylic acid, mixing it with HCO₃^- will produce CO_{2 (g)}

• can confirm it is CO_{2 (g)} if it turns limewater cloudy

melting point determination

• allows for identification of compound by comparing with literature value

• purity of compounds can be determined

simple distillation

1. mixture heated to target temp to vaporise component to be seperated

2. vapour passes through condenser

3. distillate obtained

• cannot seperate compounds with similar BP

fractional distillation

1. mixture heated to target temp to vaporise component to be seperated

2. vapour moves up the fractionating column, some condenses & flows down until hot enough to vaporise again

3. after each boil-condense cycle, the more volatile substance will be at the top

4. vapour passes through condenser

5. distillate obtained

features of the fractionating column

• colder at the top

• glass beads to increase surface area

standard solution

solution with accurately known concentration by dissolving water & a primary standard

primary standard

substance with high purity & stability

what is the volumetric glass rinsed with?

distilled water

what is the conical flask rinsed with?

distilled water

what is the volumetric pipette rinsed with?

substance it will deliver

what is the burette rinsed with?

substance it will deliver

what is the volumetric flask used for?

prepare standard solution

what is the conical flask used for?

hold the aliquot of solution that will be titrated

what is the volumetric pipette used for?

deliver an aliquot of a solution

what is the burette used for?

deliver the solution

equivalence point

two reactants have reached correct mole proportions

• estimated by the end point

end point

permanent colour change

mass spectrometry

investigation and measurement of masses of isotopes, molecules and molecular fragments by ionising samples & seperating fragments produced using electric and magnetic fields

• only positively charged ions detected

• measures the mass-to-charge ratio (m/z) of particles

ionisation

• generates molecular ion by bombarding sample with high energy e^-

• M _(g) + e^- → M⁺ _(g) + 2e^-

fragmentation

• unstable molecular ions produce a variety of smaller ions as bonds are broken

• fragmentation pattern can help determine structure of original molecule

molecular ion

positive ion produced by ionisation of a whole molecule

the isotope effect

generation of multiple peaks for fragments with the same formula due to presence of isotopes of constituent elements

infrared (IR) spectroscopy

spectroscopy that deals with infrared region of the electromagnetic spectrum

• allows for identification of functional groups, single, double, triple bonds

• identifies specific energy absorbed by the various covalent bonds present when exposed to radiation in the IR portion

vibration of covalent bonds

• ‘ground state’

• ‘excited-state’

fingerprint region

region below 1500cm^-1 containing a pattern of peaks specific for an individual molecule

factors affecting bond vibration energy

• strength of bonds

• mass of atom

strengths of bonds

• stronger bonds require more energy to change their vibration

  → higher frequency, higher wave number

mass of atom

• bonds between lighter atoms require more energy to change their vibration

  → higher frequency, higher wave length

fundamentals of NMR spectroscopy

1. when placed in an external magnetic field, most nuclei will line up with the field (low-energy), although some will have enough energy to line up against the field (high-energy)

2. radio waves are provided to change the spin state of the nuclei from the low-energy to high-energy alignment

3. when a nucleus moves back to the low-energy alignment, it releases the specific energy difference between the two states

shielding & chemical environments

• e^- surrounding the nucleus will shield it from magnetic field

• nuclei connected to the same atoms are in the same chemical environment

  → produce one NMR signal

chemical shift

horizontal scale on an NMR spectrum

• represents difference in energy required to flip a nucleus in a sample compared to TMS

TMS

• all NMR produced are compared to a sample (TMS)

• added to samples prior to analysis, producing single peak for ¹H- & ¹³C-NMR

• value for TMS set to 0 & position of signal generated is known as chemical shift

advantages of TMS

• signal peak away from other peaks

• volatile, easily recovered

• allows data from different NMR spectrometers to be compared

low-resolution proton NMR

includes:

• number of peaks indicate the number of unique hydrogen environments

• ratio of areas under peaks shows ratio of hydrogen atoms in that environment

• chemical shift provides information about specific environments

high-resolution proton NMR

• provides same information as low-resolution proton NMR

• ¹H nuclei can react with other ¹H nuclei, and if in different chemical environments, interaction may cause original peak to split into multiple peaks

  → because neighbouring nuclei have small magnetic effect on each other

• n+1 rule

n+1 rule

for simple molecules, number of peaks is one more than number of hydrogen atoms on neighbouring carbons