Noncovalent Interactions & Water Flashcards
(12 cards)
1
Q
Strength of covalent bonds
A
200-800 kJ mol
2
Q
Properties of noncovalent bonds
A
- strength of <30 kJ mol
- based on unequal sharing of electrons between nuclei = polarised bonds and polar molecules
- intermolecular and intramolecular interactions = determine solubility in water
3
Q
Order of electronegative atoms
A
H < C = S «_space;N < O
S, N and O form polar covalent bonds
4
Q
Types of noncovalent interactions
A
- Van der Waal forces
- Hydrophobic interactions
- Charge-charge interactions (ion pairs)
- Dipole-dipole interactions and hydrogen bonds
5
Q
Hydrogen bonds in water
A
- forms 4 bonds
- central water molecule acts a hydrogen donor (x2)
- central water molecule acts as hydrogen acceptor (x2)
6
Q
Groups that are hydrogen donors
A
Amino (NH)
Hydroxyl (OH)
7
Q
Groups that are hydrogen acceptors
A
N=R
O
O=R
8
Q
Properties of hydrogen bonds
A
- most common type of dipole-dipole interaction
- 30 kJ mol strong
- H atom is bonded to an electronegative atom and can bond to another electronegative atom with a lone pair
- only strong if all 3 atoms are aligned
9
Q
Properties of charge-charge interactions
A
- Ionic bonds
- Electrostatic interactions between opposite charges
- Stronger than hydrogen bonds
- Can extend over greater distances than other noncovalent interactions = don’t rely on geometry
10
Q
What are Van der Waal forces?
A
Act between permanent dipoles or induced dipoles
Only strong if atoms are close
11
Q
Properties of VDW forces
A
- attraction between stable or inducible dipoles
- only works at very short, optimal distances
- much weaker than other dipole interactions but a large number of interactions add up to significant stabilising force in biomolecules
12
Q
What are hydrophobic interactions?
A
These are NOT bonds
Not based on attractive forces between molecules
Association of non-polar groups with the most energy attributed to the exclusion of water (increased entropy)
