1. Covalent bonds Flashcards
How many bonds can carbon, nitrogen and oxygen make?
4
3
2
What is electron delocalisation?
•Benzene: carbon-carbon bonds shifting between being double and single bonds
Electrons from double bonds are delocalised= forms regions above and below the plane of carbon skeleton
Chemically: like single bonds
Geometry: Double bonds
Do metals prefer to form chemical bonds or lose electrons? What about highly electronegative elements such as fluorine and chlorine?
Metals:
Lose electrons- Like to form positively charged ions
Highly electronegative elements:
Gain electrons- Like to form negatively charged ions rather than share electrons in a chemical bond
Example: NaCl does not exist as a molecule= Ion pairs Na+ and Cl-
What does the carbon skeleton do?
It is fairly unreactive BUT gives shape to overall molecule
Non-polar & insoluble in water but can oxidise
What are some properties of single and double carbon-carbon bonds?
C-C bonds: Unreactive and difficult to break + bond is able to rotate
C=C: Reactive + Can be converted to C-C single bonds if things are added to the carbon atoms + Rigid as cannot rotate around the bonds
Functional Groups
Group 1: Oxygen-containing
1) What are some properties of C-O bond?
2) What type of compounds are those containing hydroxyl groups?
3) What is a carboxyl group made of?
4) What is an aldehyde made up of?
5) What is a ketone made up of?
1) Strong and Stable, polar and chemically reactive
2) Alcohols and Ethers
3) Carbon atom linked to oxygen by a double bond: C=O
4) C=O and hydrogen atom linked to C and R
5) C=O, R and R
Functional Groups
Group 1: Oxygen-containing
1) What happens to the solubility of the compound when a carboxyl group is added?
2) Which is more reactive- aldehydes or ketones?
3) What happens to the C=O bond when a reaction occurs?
4) What happens when an aldehyde or ketone is added to water?
1) Makes it more water soluble
2) Aldehyde
3) Normally becomes C-O single bond
4) -Water molecule gets added to the carboxyl group:
- C=O becomes HO-C-OH for aldehyde or HO-C-OR
- Forms dihydroxyl alcohols which are unstable + reaction is spontaneously reversible
- Reaction normally favours left side of equation (separate molecules)
Functional Groups
Group 1: Oxygen-containing- Carboxylic Acids and esters
1) How can a carboxylic acid be formed from an aldehyde?
2) What happens when you add a carboxylic acid to water?
3) How is an ester made from a carboxylic acid?
4) What are some properties of esters?
1) Oxidation of aldehyde= Oxygen added to the hydrogen atom
2) -Ionisation of the hydroxyl group is favoured (loses hydrogen) which stabilises the negative charge between the 2 oxygen atoms
- COO- group is acidic= Donates protons to water + is polar
3) Hydroxyl group is replaced by alcohol: RO-C=O + H2O
4) Non-polar
Inert
Non-water soluble
Functional Groups
Group 2: Nitrogen-containing: Amines and Amides
1) How are amines derived?
2) What charge do they carry?
3) What are some properties of amines?
4) How are amides derived?
5) What are some properties of amides?
6) What is the geometry around nitrogen?
1) Derived from AMMONIA- replacing 1 or more hydrogens from NH3 with carbon skeletons
2) Can form bond with proton= Positively charged ion
Very weak bases= Accept protons
3) Polar + Water soluble
4) Carboxylic acids: Hydroxyl group is replaced with an amine (-NH2)= H2N-C=O
5) Non-charged + Does not ionise= Oxygen atom prevents N gaining or losing a proton
Polar + Can act as both donor and acceptor for hydrogen bond formation + can make carbon skeleton more water-soluble
6) Tetrahedral- 3 single bonds point towards the three corners + other corner is occupied by a pair of electrons in a filled orbital
Functional Groups
Group 2: Nitrogen containing- C=N bonds
1) What are some properties of C=N bonds?
2) What are Schiff bases?
3) How do nitrogen atoms in rings involved in C=N react?
1) Very reactive + Unstable
2) Nitrogen equivalents of aldehydes and ketones e.g.
R-C=N-H
-Intermediates in conversions of one compound to another
-Stabilised by binding to enzyme + Rarely occur in free solution
3) May be able to accept proton= basic properties BUT are generally much weaker bases= Generally carry no charge
Functional Groups
Group 3: Sulphur-containing: Thiols, Thioethers and disulphides
1) What are thiols?
2) What are thioethers?
3) How can Sulphur-Sulphur bonds be formed in thiols?
4) What kinds of valencies do sulphur show?
5) What are thioesters and what kinds of properties do they show?
6) What are sulphates used for?
1) Sulphur equivalent to alcohols: -SH group is attached to the carbon skeleton instead of -OH + Can donate protons to water= WEAK ACIDS
2) Sulphur equivalent of ethers: UNREACTIVE + NON-POLAR
3) Thiols must be oxidised= Hydrogen atom removed by oxidising agent
4) 2,4 or 6 but is usually 2-valent in biological molecules
5) Equivalent of esters: Carboxylic acid has reacted with thiol + Are highly reactive and hydrolyse readily
6) Increase polarity and water solubility
Functional Groups
Group 3: Phosphorus-containing- Phosphoric groups and phosphate esters
1) What are some properties of phosphoric acid (PO4H2)?
2) How are phosphoric groups formed?
3) What kinds of valencies do phosphorus show?
4) What is the geometry around phosphorus in phosphates and phosphoryl groups?
1) Can undergo ionisation 3 successive times= Each time donating protons to water and each one has a different pKa= Strong and weak acid
2) OH group removed from phosphoric acid= One bond to phosphorus is unoccupied
3) 3 or 5 but will always show 5 in biological molecules
4) Tetrahedral: 4 bonds are of equal length due to electron delocalisation but the double bond is not associated with a specific oxygen atom + P-O bonds have partial double bond character
Functional Groups
Group 5: Metals
1) What are the 2 major roles metals play in biological molecules? i) In ion pairs
2) ii) in complexes
1) Ion pairs: E.g. Sodium2+ and potassium+
Metal ions: Positive charge + associate with negative charges carried in biological molecules
Some proteins contain metal ions which are protected from water solvent
2) Complexes e.g. iron, zinc
Form weak chemical bonds with the biological molecule + can form template around which biological molecule shapes itself
