Exam 1 Flashcards Preview

Chem 203 > Exam 1 > Flashcards

Flashcards in Exam 1 Deck (106)
Loading flashcards...
1

What is a chemical reaction?

Electrons moving between orbitals

2

What does a line represent in a Lewis structure?

Valence electrons being stabilized by two nuclei coming together

3

What is a chemical bond?

Attraction of electrons being stabilized by other nucleus

4

Weak bond BDE

40 kcal/mol to break

5

Strong bond BDE

100 kcal/mol to break

6

What does negative enthalpy mean?

Heat is given off

Bonds formed have lower energy than original bonds

We like this

7

What two factors does covalent bonding rely on?

Orbital overlap

Energy match

8

Schrodinger equation

explains how electrons behave

allows us to generate wavefunction

9

How many nodes does an orbital have?

1s = 0 nodes
2s = 1 node (radial)
2p= 1 node (angular at nucleus)
3s=2 nodes
3p=two nodes

10

What indicates a p-orbital on a wavefunction graph?

A node at the nucleus

11

Spherical/radial node

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

12

Characteristics of destructive interference

Produces an antibonding orbital

There is a node directly between two atoms

13

Characteristics of constructive interference

Produces a bonding orbital

There is stabilization from the two waves coming together

14

Sigma H2 bond strength

104 kcal/mol

Strong bond!

15

Sigma C-C bond strength

85-90 kcal/mol

16

Sigma bond rotation in alkane energy

3kcal/mol

17

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

18

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

19

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

20

Can you have sigma bonds with p-orbitals?

Yes, if they arrange end to end

21

Lewis acid

electron pair acceptor

unoccupied orbital

we care about the LUMO

22

Lewis base

electron pair donor

occupied orbital

we care about the HOMO

23

Why is two OMOs coming together always destabilizing?

Because electrons will have to be placed in the antibonding orbital

24

Can 3 electrons coming together bond?

Yes because only 1 would have to be placed in the antibonding orbital

25

Functionality of bonds?

Unusual HOMO and/or LUMO compared to C-C bond or C-H bond of alkanes

26

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

27

What can be an unusually high HOMO?

Sigma, pi, or lone pairs

28

What can be an unusually low LUMO?

Sigma*, pi*, or empty atomic orbital

29

Why does SN2 reactions favor 1º carbons?

There is room for the nucleophile to physically access the LUMO

30

What proves the backside attack of a SN2?

chirality

an assymmetric carbon will feature inversion