Flashcards in Exam 1 Deck (106)
What is a chemical reaction?
Electrons moving between orbitals
What does a line represent in a Lewis structure?
Valence electrons being stabilized by two nuclei coming together
What is a chemical bond?
Attraction of electrons being stabilized by other nucleus
Weak bond BDE
40 kcal/mol to break
Strong bond BDE
100 kcal/mol to break
What does negative enthalpy mean?
Heat is given off
Bonds formed have lower energy than original bonds
We like this
What two factors does covalent bonding rely on?
explains how electrons behave
allows us to generate wavefunction
How many nodes does an orbital have?
1s = 0 nodes
2s = 1 node (radial)
2p= 1 node (angular at nucleus)
What indicates a p-orbital on a wavefunction graph?
A node at the nucleus
Occurs when the graph passes 0 and switches from positive to negative, but does not happen at the nucleus
s-orbitals can have spherical nodes
Characteristics of destructive interference
Produces an antibonding orbital
There is a node directly between two atoms
Characteristics of constructive interference
Produces a bonding orbital
There is stabilization from the two waves coming together
Sigma H2 bond strength
Sigma C-C bond strength
Sigma bond rotation in alkane energy
Bond rotation in alkene energy
Can't rotate alkene double bond because of pi-bond
Have to break the bond to rotate
BDE is 65 kcal/mol
Tricks for choosing the most acidic proton
Not going to be on the alkene, cause going to go in an orthogonal orbital
Want protons that are next to vinyl carbon
Draw conjugate base and look for delocalization through pi-system
Pi-system will be interrupted by sp3 hybridization
Why does carbon not use s2p hybridization?
could only make one orbital
need 2/3 s. Carbon only has 2s orbital to work with and if 2/3 of it are used up it would not be able to make another s2p
Can you have sigma bonds with p-orbitals?
Yes, if they arrange end to end
electron pair acceptor
we care about the LUMO
electron pair donor
we care about the HOMO
Why is two OMOs coming together always destabilizing?
Because electrons will have to be placed in the antibonding orbital
Can 3 electrons coming together bond?
Yes because only 1 would have to be placed in the antibonding orbital
Functionality of bonds?
Unusual HOMO and/or LUMO compared to C-C bond or C-H bond of alkanes
Why is a lone pair an unusually high HOMO?
It is not getting stabilized by another atom
So this makes it an unusually high HOMO
What can be an unusually high HOMO?
Sigma, pi, or lone pairs
What can be an unusually low LUMO?
Sigma*, pi*, or empty atomic orbital
Why does SN2 reactions favor 1º carbons?
There is room for the nucleophile to physically access the LUMO