chapter 9

Question 1

alkane numbering:

Answer 1

• 1C = methane
• 2C = ethane
• 3C = propane
• 4C = butane
• 5C = pentane
• 6C = hexane
• 7C = heptane
• 8C = octane
• 9C = nonane
• 10C = decane

Question 2

groups attached to alkanes to know:

Answer 2

• methyl CH₃-R
• ethyl CH₃CH₂R
• propyl CH₃CH₂CH₂R
• butyl CH₃CH₂CH₂CH₂R
• isopropyl
• sec-Butyl
• tert-butyl

Question 3

list of functional groups priority:

Answer 3

• carboxylic acid
• ester
• acyl chloride
• amide
• aldehyde
• ketone
• alcohol
• thiol
• amine
• alkyne
• alkene
• alkane

Question 4

carboxylic acid:

Answer 4

• prefix: carboxy
• suffix: oic acid

Question 5

ester:

Answer 5

prefix: oxycarbonyl
suffix: oate

Question 6

acyl chloride:

Answer 6

prefix: halocarbonyl
suffix: oyl halide

Question 7

amide:

Answer 7

prefix: carbamoyl
suffix: amide or carboxamide

Question 8

aldehyde:

Answer 8

prefix: oxo or formyl
suffix: al or carbaldehyde

Question 9

ketone:

Answer 9

prefix: oxo
suffix: one

Question 10

alcohol:

Answer 10

prefix: hydroxy
suffix: ol

Question 11

thiol:

Answer 11

prefix: mercapto
suffix: thiol

Question 12

amine:

Answer 12

prefix: amino
suffix: amine

Question 13

alkyne:

alkene:

alkane:

Answer 13

prefix: alkynyl
suffix: yne
prefix: alkenyl
suffix: ene
prefix: alkyl
suffix: ane

Question 14

resonance structures are attempts to represent?

Answer 14

• the underlying form of the molecule, in which the electrons are delocalized
  
  • electron delocalization can significantly affect the chemical properties of a compound

Question 15

a special case of resonance is known as?

Answer 15

• conjugation
  
  • associate conjugation with structures containing alternating single and double bonds in carbon chains
  • a characteristic of compounds with conjugated systems is that they absorb UV light and can therefore be well visualized using UV spectroscopy

Question 16

what are aromatic compounds?

Answer 16

conjugated cyclic molecules with a planar structure that also satisfy an additional criterion known as Huckels tule: having 4n + 2Π electrons, where n is an integer

Question 17

what are isomers?

Answer 17

• molecules that share the same molecular formula but differ in their structure

Question 18

the general topic of how molecules are arranged in space in different ways is known as?

Answer 18

• stereochemistry

Question 19

what are structural/constitutional isomers?

Answer 19

• refers to the different ways that aroms can be connected with each other given a single molecular formula
  
  • no way to predict the number or configuration of structural isomers by looking at the molecular formula so you have to draw them out and they can have fundamentally different chemical properties

Question 20

structural isomers with different functional groups are known as?

Answer 20

• functional isomers

Question 21

what are tautomers?

Answer 21

• this term refers to structural isomers that interconvert with each other and exist in equilibrium
  
  • ex. keto-enol isomerism
  • enamines and imines
  • lacrams and lactims
  • amides and amines
    
    • not the same as resonance because tautomers are 2 different structures that interconvert via the breaking and re-formation of bonds

Question 22

what are stereoisomers?

Answer 22

• describes how molecules within a single pattern of connectivity among their constituent atoms can have different spatial configuration (subset of a single structural isomer)
  
  • arrangements around single bonds- single bonds can rotate without being broken and some of the resulting configurations known as conformational isomers are more favourable than others (Newman projections)
  • orientation across a double bond- a substituent can be located on one side or another of a double bond and the terms cis/trans and E/Z system describe this
  • orientation at a chiral center- 4 different sub’s on a C and multiple systems exist for describing such orientations, most notably the R/S system and the d/l (+/-) system

Question 23

Newman projections are used to show?

Answer 23

conformational isomers

Question 24

another type of conformational isomerism arises in?

Answer 24

• cyclohexanes due to:
  
  • angle strain- occurs when the angle between single bonded C atoms deviate from 109.5°
  • torsional strain- created by eclipsing substituents on neighbouring atoms
  • steric strain is caused by substituents getting in each other’s way
    
    • in order to resolve these forms of strain, cyclohexane alternates between chair, boat and twist-boat

Question 25

the substituents of cyclohexane can either be in an?

Answer 25

• axial or equitorial orientation
  
  • bulkier substituents are placed equitorially

Question 26

if a cyclohexane ring has 2 substituents that both point up or down, it is referred to as?

if the 2 subs point in different directions, then the configuration is referred to as?

Answer 26

• cis
• trans
  
  • the cis and trans substituted cyclohexanes are stable
  • a cis isomer cannot be converted to a trans isomer without breaking and reforming a bond however, the chair conformation of each of these isomers can interconvert in order to optimize steric hindrance

Question 27

what is geometric isomerism?

Answer 27

• deals with the spatial orientation of atoms around a double bond
  
  • C=C bonds have a fixed planar shape
    
    • cis trans and E/Z classification
      
      • cis and trans isomers are used for when both substituents are the same on either the same side or opposite from each other
      • Z and E isomers are used for pointing out whether the 2 highest priority substituents are on the same (Z) or opposite sides (E)

Question 28

the number of stereoisomers that are possible for a given structure is equal to?

Answer 28

2ⁿ where n is the number of stereocenters

Question 29

what are meso compounds?

Answer 29

• molecules that have multiple stereocenters but are not chiral because they have a plane of symmetry running through the molecule that divides it into 2 superimposable mirror images

Question 30

the solutions of chiral compounds rotate planes of polarized light at angles unique to each compound. this is defined as?

Answer 30

• the specific rotation (alpha) of the molecule
  
  • compounds that produce clockwise rotations (+) of plane-polarized light are dextrorotatory (d) and compounds that produce counterclockwise (-) rotation are levorotatory (l)
  • the specific rotation of a chiral compound in solution can be calculated by:
    
    • [alpha] = a/cl
      
      • a is the observed roation, c is the concnetration in g/nL and l is the length of the polarimeter tube

Question 31

a mixture with an equal 50:50 composition of 2 enantiomers of a given compound is known as?

Answer 31

• a racemic mixture
  
  • such mixtures do not rotate plane-polarized light because they cancel each other out

Question 32

we can work backwatds from the observed rotation of a mixture- if we know [alpha]- to calculate the distribution of enantiomers in a solution using this formula:

Answer 32

enantiomeric excess (%) = [alpha]_observed/[alpha]_pure x 100

Question 33

how to figure out the R and S configuration of chiral centers:

Answer 33

1. assign priorities to each substituent. recall that aotms with greater atomic weights receive higher priority
2. if the lowest priority substituent is in the back, move to step 3. if not, draw the lowest priority so that it is in the back
3. determine whether the order of substituents from highest to lowest priority runs clovkwise (R) or counterclockwise (S) direction
4. if the orientation of the lowest priority group was changed in step 2, then the true absolute configuration will be the opposite of that found in step 3

Question 34

enantiomers vs diastereomers:

Answer 34