Alkanes, Cycloalkanes and Alkyl Halides

Question 1

only hydrogens and sp3 hybridised carbons is true about ________ hydrocarbons:

Answer 1

saturated

Question 2

n-alkanes (“normal” alkanes):

Answer 2

chains of -CH2- groups (methylene groups), terminated at each end by a hydrogen atom and not branched

Question 3

Branched alkanes

Answer 3

structural isomers of n-alkanes

Question 4

n carbon atoms must contain

Answer 4

(2n + 2) hydrogen atoms

Question 5

Non-polar molecules: dissolve in

Answer 5

non-polar or weakly polar organic solvents and are hydrophobic

Less dense than water and insoluble in water

Question 6

Rotation occurs in ______ bonds, but not in _____ bonds

Answer 6

single
double

Question 7

Each structure generated by the rotation: are which type of isomer?

Answer 7

conformer or conformational isomer

Question 8

We generally draw the lowest-energy conformation: the one with
minimal ________ repulsion between bonds

Answer 8

electrostatic

Question 9

ethane - rotate?

Answer 9

120 degrees

Question 10

staggered conformation is always at what energy?

Answer 10

LOWEST

Question 11

Higher energy conformations also exist:

Answer 11

staggered conformer <> eclipsed conformer <> staggered conformer

<> = each rotate 60 degrees

Question 12

Newman projections:

Answer 12

Higher energy – torsional strain

Question 13

Conformational Equilibria-Ethane

Answer 13

We can plot energy against dihedral angle (H-C-C-H)

Question 14

Gauche:

Answer 14

all the bonds are staggered but the sub substituents, so the two methyl groups are still near one another

Question 15

How to count numbers of gauche in a compound?

Answer 15

big functional groups are near each other

(staggered not eclipsed)

Question 16

if two big groups of each other are too close to each other it will cause

Answer 16

repulsion

Question 17

Cycloalkanes

Answer 17

Alkanes that contain rings of carbon atoms

Simple cycloalkanes:
rings of -CH2- groups (methylene groups)

Question 18

General formula cycloalkanes: CnH2n
whats the general formula of alkanes?

Answer 18

CnH2n+2

Question 19

open-chain alkanes in their physical properties
and in their chemistry are called -

Answer 19

acyclic (noncyclic)

Question 20

cycloalkane has _ distinct faces

Answer 20

2

cis/trans

Question 21

geometric isomers cannot interconvert without ______
and __-______ bonds

Answer 21

breaking
re-forming

Question 22

Csp3 - bonds?

Answer 22

4 single bonds

Question 23

Csp3 shape + angle;

Answer 23

tegrahedrol + 109.5 degree

Question 24

why 109.5 degrees for Csp3?

Answer 24

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

Question 25

Conformations in cycloalkanes; two types of strain

Answer 25

angle strain and torsional strain = ring strain

Question 26

Cycloheane - flat; so wjich strain?

Answer 26

cyclohexane would suffer from angle and torsional strain

Question 27

If cyclohexane flat

Answer 27

• Internal angles 120º
• All H eclipsed

Question 28

in a chair conformation; cyclohexane

Answer 28

• All bond angles ~109.5º
• All H staggered

Question 29

Cyclohexane can _____ between chair conformations

Answer 29

flip

Question 30

Types of substituents in chair conformation:

Answer 30

Axial substituents: drawn vertically (1 on each C)

Equatorial substituents: drawn parallel (1 on each C)
to the next-but-one C-C bond

Question 31

substituents prefer to be _______ than ______

Answer 31

equatorial than axial

Question 32

_______ substituents give a greater preference for the equatorial position

Answer 32

Larger

Question 33

what occurs at equilibrium of disubstituted cyclohexane?

Answer 33

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

Question 34

if cyclohexane is 95% <> 5% what happens?

Answer 34

gauche interaction appear
Daxially interaction

Question 35

What kind of bond is carbon-halogen?

Answer 35

polar - easy to break

Question 36

Nucleophiles

Answer 36

love nuclei

Wish to form bonds by donating or sharing their electrons

are electrons rich and can be negative ions, or neutral molecules with electron lone pairs

Question 37

Electrophiles

Answer 37

love e

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 38

Curley arrows

Answer 38

way to understand reaction mechanisms

Question 39

direction of arrow

Answer 39

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 40

lone pairs are shown as

Answer 40

two dots

Question 41

single e:
Curley arrow:

Answer 41

single dot
half of the arrow with Curley tail

Question 42

e.g. C —Br (Curley arrow going from bond to the bromine), what does this show?

Answer 42

shows the carbon-bromine bond breaking

Question 43

define nucleophilic substitution:

Answer 43

nucleophile (NUC) replaces a leaving group (X-) from a carbon atom, using its lone pair of e- to from a new bond to the carbon atom

Question 44

Define Elimination reaction

Answer 44

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 45

elimination = what kind of bond will form

Answer 45

C C double bond