3.4 - Organic Analysis

Test Tube Reactions

Test Tube Reactions

What is the Positive result of a Bromine water test?

• What gives the positive result

Orange → Colourless:

• Alkenes

What is the Oxidising agent for Alcohols?

Potassium Dichromate (K₂Cr₂O₇)

What is the Positive result of Potassium Dichromate:

• Primary Alcohol

• Secondary Alcohol

• Tertiary Alcohol

Orange → Green:

• Primary → Aldehyde → Carboxylic Acid

• Secondary → Ketone

• Tertiary → N/A

What solutions can you use to differentiate Aldehydes + Ketones?

• Positive results → for both

Fehlings (Copper based solution) / Tollens (Silver mirror test) → Test for Aldehydes:

• Fehlings = Blue → Red

• Tollens = Silver mirror precipitate formed

How do you differentiate between -OH in IR Spectroscopy:

• Alcohol

• C.Acid

• Alcohol = Whale head → (more of a curve on the left of the spiky notch)

• C.Acid = Iceberg → (large + wide notch)

Define the Fingerprint region

Region in an IR Spectrogram between 500cm^-1-1500cm^-1 unique to a compound → computers can only differentiate this by comparing the sample to known compounds + finding exact matches

How do IR Spectrograms create the Spectrographs?

Bonds in molecules have their own vibrational frequencies which increase as IR is absorbed, then released and detected to form the graph

What is the IR cycle of Global Warming? (4 steps)

1. IR is emitted from the sun to earth

2. In the night as the earth cools, IR is re-emitted back out into the atmosphere → some to space

3. Molecules like C=O from Carbon dioxide absorb this re-emitted IR

4. The molecules then re-emit the IR to surrounding molecules which absorb + emit IR to the earth → having an overall net increase in Global Temperature

What 6 types of Molecules absorb IR in the atmosphere?

1. CO₂

2. H₂O

3. NO_x

4. CH₄

5. O₃

6. CFC’s

Additional Mass Spec

Additional Mass Spec

Why are HRMs used over LRMs?

HRMs have a higher Mr resolution of a higher degree → LRMs have whole number resolution so can give the same Mr for different compounds

When are HMRs useless?

Isomers with same Mr

How do we determine isomers from eachother?

• Which type of Mass Spec

Look at fragment peaks to differentiate samples, small number of whole isomer molecules are detected

• Electron Impact

Why are the fragment peaks larger than molecule peaks?

As the Mr of sample increases, the ions increase in instability so fewer number of whole isomer molecules are detected

***READ FRAGMENTATION PEAKS + M/Z FROM CHEM NOTES 2***

***READ FRAGMENTATION PEAKS + M/Z FROM CHEM NOTES 2***