Alkanes, Cycloalkanes And Alkyl Halides (w19)

Question 1

What happens to non polar molecules ?

Answer 1

Non-polar molecules: dissolve in non-polar or weakly polar organic solvents and are hydrophobic

Question 2

Non-polar molecules are ____ dense than water and ____ in water.

Answer 2

Less
Insoluble

Question 3

When does bond rotation occur in conformational isomers ?

Answer 3

Occurs in single bonds but not double bonds

Question 4

Each structure is generated by the rotation is a what ?

Answer 4

A conformer or conformational isomer

Question 5

What is GAUCHE ?

Answer 5

Gauche:
When all the bonds are staggered, but the big substituents, so the two methyl groups are still near one another

Question 6

What is the conformational equilibrium of an alkane ?

Answer 6

When the energy relative to anti conformation is plotted against the dihedral angle

Question 7

What are the two distinct faces of a cycloalkane ?

Answer 7

• two substituents point towards the same face (CIS)
• two substituents point towards the opposite face (TRANS)

Question 8

What can’t the geometric isomers of cycloalkanes do ?

Answer 8

They can’t interconvert without breaking and re-forming bonds

Question 9

What is the general formula of cycloalkanes ?

Answer 9

CnH2n

Question 10

General formula of alkanes ?

Answer 10

CnH2n+2

Question 11

What may cycloalkanes experience during conformation ?

Answer 11

Angle strain and torsional strain (ring strain), this can be reduced by deviating from a planar structure

Question 12

What does the preferred bond angle of 109.5 of a C sp3 tetrahedral carbon do to the electrons ?

Answer 12

Places the electron clouds as far away from one another as possible

Question 13

What would cyclohexane suffer from if it was flat ?

Answer 13

Suffer from angle and torsional strain.

Question 14

Can cyclohexane flip between chair conformations ?

Answer 14

Yes

Question 15

What is chair conformation ?

Answer 15

Chair
Lowest energy – all H are as far apart as possible – so is the most stable

Question 16

What is boat conformation ?

Answer 16

Boat
Unfavourable steric interactions – some H too close - and is less stable.

Question 17

What do substituents on cyclohexane prefer to be ?

Answer 17

Prefer to be equatorial rather than axial

Question 18

What do larger substituents give ?

Answer 18

They give a greater preference for the equatorial position

Question 19

What does preference of disubstituted cyclohexane depend on?

Answer 19

Depends on the substituents and their relative stereochemistry

Question 20

What occurs at equilibrium of disubstituted cyclohexane ?

Answer 20

The upper conformer dominates (98%) and both groups are equatorial

Question 21

What is the carbon-halogen bond ?

Answer 21

Polar - so is easy to break

Question 22

What are nucleophiles ?

Answer 22

• Nucleophiles “love nuclei” and wish to form bonds by donating or sharing their electrons
• Nucleophiles are electrons rich and can be negative ions, or neutral molecules with electron lone pairs

Question 23

What are electrophiles ?

Answer 23

• Electrophiles “love electrons” and wish to form bonds by accepting electrons or sharing electrons with a reactant molecule.
• Electrophiles are electron deficient and can be positive ions or neutral (but δ+) molecules

Question 24

Does a nucleophile have a lone pair of electrons or does this apply to an electrophile?

Answer 24

Nucleophiles have a lone pair of e-
- they are electron donors and electrophiles are e- acceptors

Question 25

What is nucleophilic substitution ?

Answer 25

Nucleophilic substitution: nucleophile (Nuc∶-) replaces a leaving group (X−) from a carbon atom, using its lone pair of electrons to form a new bond to the carbon atom

Question 26

What is an elimination reaction ?

Answer 26

Elimination reaction: halide ion leaves along with another atom or ion (often H+), a new pi bond results. Dehydrohalogenations (H-X). Reagent (B:-) reacts as a base. Most nucleophiles are also basic and can engage in either substitution or elimination, depending on the alkyl halide and the reaction conditions

Question 27

What are curly arrows ?

Answer 27

A way to understand reaction mechanisms and can be applied to the understating if mechanisms of biological processes and the action of drugs

Question 28

What is a double headed arrow used to show ?

Answer 28

A double-headed arrow is used to show the movement of a PAIR of electrons
(from where they are to where they are moving)

Question 29

What is a single-headed arrow used to show ?

Answer 29

Occasionally you may encounter single-headed arrow. This is used to show the movement of a SINGLE electron

Question 30

What does a single covalent bond contain ?

Answer 30

Two electrons

Question 31

Which direction does a curly arrow go ?

Answer 31

From nucleophile to an electrophile