Organic lecture 2 Flashcards
Describe sp2 hybridisation
One s and two p orbitals mix to form three identical sp2 hybrid orbitals. Each orbital is dumbbell shaped with one lobe smaller than the other, and the three have corners forming a linear equilateral triangle (trigonal orientation), and are 120 degrees apart from each other. The remaining p orbital is perpendicular to this plane.
State the multiplier given by ‘pico’
1x10^-12
Define a double bond and state its bond length in carbon
A double bond is formed of one sigma bond and one pi bond. A carbon carbon double bond is approximately 134pm
Describe sp3 hybridisation
One s and one p orbital mix to form two identical sp hybrid orbitals. Each orbital is dumbbell shaped with one lobe smaller than the other, and point at 180 degrees to each other. The other two 2p orbitals are perpendicular to each other and are in line with the sp orbitals.
Describe the bonding in ethene
Two carbon atoms form a sigma bonds and a pi bond (ie a double bond), and sigma bonds are formed between the carbon and the hydrogen atoms.
Describe the bonding in ethyne
A sigma bond is formed to the other carbon atom as the two sp orbitals overlap, and the remaining two 2p orbitals form pi bonds, forming a c-c triple bond. The remaining sp orbitals form sigma bonds with hydrogen atoms.
Define a triple bond and state its bond length in carbon
A triple bond is formed of one sigma bond and two pi bonds between the same two atoms. A carbon carbon triple bond is approximately 120pm.
Describe how to identify sp hybridisation by looking at the number of pi and sigma bonds
If a carbon atom has 2 pi bonds and 2 sigma bonds, it is sp hybridised
Describe how to identify sp2 hybridisation by looking at the number of pi and sigma bonds
If a carbon atom has 1 pi bond and 3 sigma bonds, it is sp2 hybridised
Describe how to identify sp3 hybridisation by looking at the number of pi and sigma bonds
If a carbon atom has 0 pi bonds and 4 sigma bonds, it is sp3 hybridised.
State which out of pi and sigma bonds are weaker
Pi bonds are weaker than sigma bonds.
Define the electronegativity of an element
Electronegativity is a measure of an element’s tendency to attract the electron density in a covalent bond
Describe what happens in a bond if there is a difference in electronegativity between the atoms
Bonds are polarised, as one atom will be pulling the bonding electrons more forcefully than the other. This forms a dipole, and can be shown using an arrow (->-) or with partial charges. The bigger the difference in electronegativity, the bigger the partial charges
Describe how positive charges are affected in molecules with more than two atoms
The main influence of the electronegative atom is felt by the atom(s) directly bonded to it, but its effect is felt further along the chain, although the ‘inductive effect’ falls off very quickly. It can be represented by drawing more delta signs further along the chain
Describe the inductive effect, using H-CH2-Cl as an example
The inductive effect refers to the electron withdrawing effect (due to a difference in electronegativity) through the sigma bonds of a molecule. In chloromethane, the chlorine atom would be referred to as an inductively electron-withdrawing substituent
