Alkanes + Cyclo

Question 1

According to old names a propane substituent bonded at the middle is called what?

Answer 1

Isopropyl

Question 2

What is a primary carbon?

Answer 2

One which is bonded to 1 other carbon

Question 3

What is a secondary carbon?

Answer 3

One which is bonded to 2 other carbons

Question 4

What is a tertiary carbon?

Answer 4

One which is bonded to 3 other carbons

Question 5

What happens to melting/ Boiling points as the carbon chain gets longer and why?

Answer 5

They increase due to stronger London dispersion forces

Question 6

What are London dispersion forces?

Answer 6

When electrons repel each other creating temporary delta positives and negatives, thus a temporary dipole.
Theyre really weak intermolecular interactions

Question 7

Do branched alkanes have higher or lower melting boiling points than straight chains?

Answer 7

Lower, they’re harder to pack and therefore experience less temporary dipoles (London dispersion forces)

Question 8

Are alkanes reactive?

Answer 8

Quite unreactive due to strong c-c

But can have reactions eg with chlorine gas and can be burnt (oxidisation)

Question 9

Why do we burn alkanes?

Answer 9

The c-c bond is really strong, so when burnt it releases a lot of energy which can be used.

Question 10

What is a constitutional isomer?

Answer 10

It has a different structural arrangement, different connectivity

Question 11

What is an molecule isomer?

Answer 11

Different molecules that have the same molecular formula. So can be arranged differently etc

Question 12

What does a staggered conformation mean?

Answer 12

When atoms are in the form with lowest energy. they face the least repulsion, atoms are as far apart as possible within the molecule

Question 13

What does an eclipsed conformation mean?

Answer 13

Molecule has rotated in a way in which atoms are overlapping. Electrons repel each other therefore this form is a high energy form

Question 14

What is the anti conformation?

Answer 14

When the molecule has rotated in a way in which no atoms are overlapping, it has the least repulsion between atoms and is therefore the most stable

Question 15

What is the gauche conformation?

Answer 15

When the molecule has rotated in such a way that it is staggered but there may be some groups overlapping so it is higher in energy than the anti conformation

Question 16

How can molecules have rigidity if they are constantly rotating? (eg enzymes)

Answer 16

By creating ring structures, bond ability to rotate is significantly decreased

Question 17

Why are many enzymes cyclic?

Answer 17

Cyclic bonds are harder to rotate and are therefore more rigid

Question 18

Are cycloalkanes isomers of the linear version?

Answer 18

No there is normally two less hydrogens, different molecular formula

Question 19

Why are 6 membered rings the most common?

Answer 19

They experience the least ring strain.

Question 20

What is torsional strain?

Answer 20

strain in a ring caused by trying to avoid eclipsing. (ring puckers)

Question 21

What is steric ring strain?

Answer 21

When the bulkiness of the groups causes them to be close

Question 22

What is angle strain?

Answer 22

When the ring forms angles that deviate from the common carbon tetrahedral 109.5 degrees

Question 23

What has lower energy the boat or the chair conformation? and why?

Answer 23

Chair has lower energy as the atoms are more staggered, they face less repulsion and are therefore more stable

Question 24

Why does boat conformation have higher energy than chair?

Answer 24

It has more torsional strain. Groups closer together

Question 25

What is lower in energy equatorial position or axial?

Answer 25

equatorial as it can be further from other atoms

Question 26

Why do most rings once in chair conformation normally stay in chair?

Answer 26

It is the lowest energy form, also the energy cost to get to half chair form is really high

Question 27

What is thermodynamically more stable, CIS or TRANS?

Answer 27

Trans as they are on opposite sides, therefor face less repulsion

Question 28

What kind of isomers are cis and trans?

Answer 28

Stereoisomers

Question 29

What is a stereoisomer?

Answer 29

orientation in space is different. Put together in the same way.

Question 30

What is a constitutional isomer?

Answer 30

Same molecular formula but different connectivity

Question 31

with a longer chain of alkane is it more or less likely to be solid?

Answer 31

More likely since more intermolecular forces (London dispersion forces)

Question 32

What is electronegativity?

Answer 32

How good it is at pulling electrons towards itself

Question 33

Order of strength of forces

Answer 33

Covalent
ionic
hydrogen
dipole-dipole
induced-dipole
induced-induced (London)

Question 34

Do branched or linear alkanes have higher melting points?

Answer 34

Linear have higher melting points since they can pack better so more intermolecular forces

Question 35

Why do spontaneous reactions happen?

Answer 35

products are more stable than reactants so more energy given out then needed to break or make the bonds