Lecture 3: Polarity Flashcards
(41 cards)
What does a molecule require to be polar?
A dipole moment and an assymetrical structure
What is a dipole moment?
The sum of individual bond polarities and lone pair contributions within the molecule
What are polar molecules?
Hydrophillic: Water-loving and Fat-hating
What do polar molecules have?
high melting and boiling points
Why do polar molecules have high melting and boiling points?
Due to the dipole-dipole interactions, which are strong bonds that require a large amount of energy to break
What is an example of a dipole-dipole interaction?
CH3CL – CH3CL: Methyl Chloride
- Chlorine is electro-ve, so all electrons surround the chlorine mol.
- Chlorine has a permanent negative charge/dipole
-Methyl group has a permanent positive charge/dipole as it’s deprived of electron
- When +ve methyl group contacts a -ve chlorine group, produces a dipole-dipole interaction.
How does a dipole moment affect the melting and boiling points of a molecule?
Stronger interaction between molecules = Greater dipole moment.
Greater dipole moment = More energy required to break bonds
What are hydrogen bonds?
Occur between hydrogen molecules and oxygen,nitrogen and fluorine groups.
Why are hydrogen bonds so strong?
Hydrogen molecules are very strong and have no electrons protecting their nucleus.
Therefore the bonds form very close to the nucleus, producing high boiling and melting points.
What is an example of a hydrogen bond?
2 water molecules: H2O- H2O
- Oxygen is electronegative, so electrons surround it
- Oxygen therefore has a permanent negative charge/dipole
-Hydrogen has a permanent positive charge/dipole as they are deprived of electrons
- A hydrogen bond then forms between the negative oxygen and the positive hydrogen
What are non-polar molecules?
Hydrophobic: Water-hating and fat-loving
What do non-polar molecules dissolve and extract in?
non-polar solvents
Why do non-polar molecules have lower boiling and melting points than polar molecules?
The forces between molecules are London dispersion forces/Van der whaal’s forces
These forces are weak and easily broken
Why must samples be extracted?
Samples are composed of an analyte of interest and a matrix.
The analyte must be extracted into a solvent to be analysed
How is extraction used to produce pure samples?
Extraction is used to remove contaminants from a sample.
*Substances must be pure to be analysed
How is extraction used to increase concentration?
Crime scene samples may be so small they’re under the limit of detection.
Extraction can increase concentration
What are the issues with extraction?
- A sample with a large no. of analytes - can be difficult to extract one
- Small sample: Sample can be lost
- Chemical similarities between samples: Difficult to extract one
What are the methods of extraction?
- Liquid-liquid
- Liquid-solid
- Solid phase
- Solid phase micro extraction
What is liquid - solid extraction?
Extracting a solid powder into a liquid e.g. extracting cocaine into a non-polar solvent
What is liquid-liquid extraction?
A liquid sample is partitioned into another liquid sample.
Using a separating funnel containing an aqueous layer and a non-polar layer
What is the method for liquid-liquid extraction?
- Add sample to funnel
- Remove the funnel from ‘O’ ring and shake
- Open valve to release pressure
- Place back in stand & allow layers to equillibriate
- Remove seperate layers into 2 conical flasks
- Evaporate to dryness under nitrogen
What is liquid-liquid extraction dependant on?
- The polarity of the analyte: Polar extracts into polar solvents. non-polar extracts into non-polar solvents
- pH: Specific pH used to analyse acidic, alkali and neutral drugs
What does log P determine?
How polar or non-polar a drug is
What does log P involve?
Liquid-liquid extraction using oil and water
-Hydrophobic drugs extract into the oil
-Hydrophillic drugs extract into the water
