Lecture 1

Question 1

what is the Lewis structure?

Answer 1

Structural formulas showing all valance electrons and formal charges

Question 2

a tetrahedral has a bond angle of

Answer 2

109.5

Question 3

what is Hybridisation

Answer 3

it is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for pairing of electrons to form chemical bonds

Question 4

What are the 3 Types of Hybridisation (that i need to know about now)

Answer 4

1. sp^1
2. sp^2
3. sp^3

Question 4

describe the sp orbitals stability

Answer 4

sp orbitals are more stable than the p orbital and less stable than the s orbital

(sp^1>sp^2>sp^3)

Question 5

what is the sp^3 orbital

Answer 5

it is a hybrid between the valance orbital of one 2s and 3 2p orbitals mixed that form 4 valance shells each with 1 electron in which they are spatially arranged to form a tetrahedral

Question 6

what is the sp^2 orbital

Answer 6

it is a hybrid between the valence orbitals of 1 2s and 2p that forms 3 valence shells each with one electron at which they are spatially arranged to form a trigonal planar with a (120 degree), In this structure one P orbital is left out

Question 7

which is stronger a pi bond or a sigma bond and why

Answer 7

A sigma bond

because pi bonding has less overlap

Question 8

alkane C-H bonds are made from the overlap of which orbitals

Answer 8

sp^3 —– s

Question 9

alkane C-C bonds are made from the overlap of which orbitals

Answer 9

sp^3 —- sp^3

Question 10

alkene C-H bonds are made from the overlap of which orbitals

Answer 10

sp^2 —- s

Question 11

alkene C=C bonds are made from the overlap of which orbitals

Answer 11

sigma: sp^2 —sp^2
Pi bond: the p orbital left from hybridization

Question 12

What is a sp^1 orbital

Answer 12

it is a hybrid orbital between 1 2s and 1 2p where it has 2 valence shells with one electron in each, at which it is specially arranged to format a linear structure (180 degrees). In this structure, two P orbitals are left

Question 13

alkynes C-H bonds are made from the overlap of which orbitals

Answer 13

sp—s

Question 14

alkynes C≡C bonds are made from the overlap of which orbitals

Answer 14

1 Sigma: the overlap of sp—sp
2 Pi bonds (each one): The overlap of the 2 p orbitals left from hybridization.

note: the two Pi bonds are perpendicular (linear bond is 180)

Question 15

the dashed bond line represents

Answer 15

the element going away you

Question 16

the full bond line represent

Answer 16

the element coming towards you

Question 17

How to draw the sawhorse structure

Answer 17

look the the 3D structure of the molecule from a diagonal view

Question 18

How to draw the Newman structure

Answer 18

look at the 3D model of the molecule from a straightforward position

Question 19

rotation in organic molecules can only occur around

Answer 19

Single bonds except for single bonds in cyclic structure due to the ring structure

Question 20

what are conformers

Answer 20

they are the same molecules, but different in 3D orientation as they are interconvertible (can change into each other by rotation of about 60 degrees)

Question 21

what are the two types of conformers we need to know

Answer 21

Staggered and eclipsed conformers

Question 22

what is the difference between staggered and eclipsed conformers

Answer 22

staggered is where the carbon across is rotated 60 degrees away from the other carbon at which there is small amounts of repulsion between the atoms.

Eclipse is where the carbon is rotated 60 degrees towards the other carbon at which the molecules attached to the carbons are stacked together so a lot of repulsion occurs which isn’t energetically favorable.

Question 23

How do you get from staggered to eclipsed conformers

Answer 23

it doesn’t require any reaction just a rotation of 60 degrees around the carbon but some energy might be required as not all conformers have the same energy as in eclipsed form they are way more repulsion between the orbitals.

Question 24

Draw staggered and eclipsed conformers

Answer 24

draw them :) Page 24 lecture 1

Question 25

What is Steric strain/hindrance, how can it be increased, and how can it affect the eclipsed and staggered conformers

Answer 25

it is the repulsion between electron clouds of atoms and groups, and it is increased by more substituents. Due to more substituents some conformers might need more energy to be made as repulsion between a hydrogen - hydrogen electron cloud is less than the repulsion between a alkyl- alkyl electron clouds

Question 26

why do cyclic structures have weaker bonds

Answer 26

due to poor overlap causing deviation form 109.5 and angle strain

Question 27

as the cyclic chain gets bigger what happens to the stability of the ring and why

Answer 27

the stability increases with more bonds (with the exception of cyclohexane being the most stable) there is more freedom in movement meaning less steric strain (angle strain) in the molecule so it is more energetically favorable for example cyclopropane has very high steric strain as all its hydrogens are eclipsed but with cyclobutane, we are allowed more movement so it can be twisted to minimize the angle strain and the number of eclipsed hydrogens

Question 28

what is cyclohexane chair conformer

Answer 28

it is the ideal ring structure that is completely free of strain with a bond angle of 111 (Degrees) and all adjacent bonds are staggered.

Question 29

how do you draw cyclohexane chair conformer normal and flipped and in Newmen projection

Answer 29

slide 30 and onward on lecture 1 :)

Question 30

what is one property of cyclohexane chair conformers

Answer 30

they can interconvert between two stable chair conformers at which the ring flips and the axial bonds become equilateral and vice versa

Question 31

what is the process of changing between the two stable chair conformers

Answer 31

so it is a process that requires no reaction at all, but it does require energy, What we do is we keep folding the chair conformer until we flip it completely, it goes from chair to half chair requiring more energy then twist-boat requiring less energy then to boat requiring more energy then to twist-boat requiring less energy then to half chair requiring more energy then back to chair requiring less energy Note boat doesn't require as much energy as half-chairs

Question 32

in chair conformers, most steric strain/hindrance occurs in?

Answer 32

the axial position, so for a more stable structure we want the larger groups to be equatorial

Question 33

what is a boat conformer

Answer 33

another stable conformer of cyclohexane with almost no angle strain, but it isn't as stable as chair conformers as some of the C-H bonds are ellipsed and because of the close proximity of the flagpole hydrogen

Question 34

what are 1-3, diaxial interactions

Answer 34

it is the unfavorable steric interactions between the parallel axial bonds that are relative on each other on the 1,3 position