23. The concept of isomerism, types of structural isomerism, nomenclature of organic compounds

Question 1

What are isomers?

Answer 1

Compounds with same formula but different structure

Question 2

3 forms of isomerisms

Answer 2

1. Constitution → Order / sequence of atoms: which atom is connected to which other one by covalent bond
2. Configuration: Spacial structure of atoms that are directly connected to each other (that are connected to one specific C)
3. Conformation: Spacial structure of atoms that are directly not connected to each other

Question 3

What is constitution?

Answer 3

Order / sequence of atoms: which atom is connected to which other one by covalent bond

Question 4

What are the 3 types of constitutional isomerism?

Answer 4

1. Branching/ backbone isomers
2. Positional isomers
3. Tautomers

Question 5

What is keto-enol tautomerism

Answer 5

A type of constitutional isomerism that refers to a chemical equilibrium between the keto form (carbonyl structure containing α-hydrogen) and the enol form (a double bond adjacent to an alcohol, -C=C-OH) of a compound

Question 6

What is keto form?

Answer 6

(carbonyl structure containing α-hydrogen

Question 7

What is an enol form?

Answer 7

a double bond adjacent to an alcohol, -C=C-OH)

Question 8

What is configurational isomerism?

Answer 8

Spacial structure of atoms that are directly connected to each other (that are connected to one specific C)

→ 2 types: optical and geometric isomers

Question 9

What is stereoisomerism? (optical)

Answer 9

asymmetric compound with no symmetry axis and no plan of symmetry

→ these compounds mirror each other

=> A.K.A chiral compounds

Question 10

How does Fischer-projection work?

Answer 10

• Most oxidized C is on the top
• C-chain is vertical
• C-C bonds trend backwards, where as OH and H trends forwards

Question 11

What are the 2 types of chiral compounds?

Answer 11

L- and D-

Question 12

How does Cahn-Ingold-Prelog (CIP-) projection work?

Answer 12

• 4 groups are sorted by atomic number
• Last group - put to the back
  
  • counterclockwise
• remaining 3 groups - in one plan - in front of chiral C atom
  
  • clockwise

Question 13

Cahn-Ingold-Prelog (CIP-) projection

How does ranking of groups work?

Answer 13

• According atomic number
• if 2 or more of them are identical → the rule applied to next atom

Question 14

What are prochiral compounds? (stereoisomerism)

Answer 14

Compounds containing C-atom with 3 different groups

=> They are also achiral

Question 15

What are enantiomers?

Answer 15

• A type of configurational isomer
  
  • Compounds that are mirror image to each other
  • Identical achiral property
  • Rotate polarized light in opposite direction
  • different when they react with other chiral compounds

Question 16

What is racemic mixture (racemate)?

Answer 16

Mixture that contains equal amounts (5-%-50%) of 2 enantiomers

Question 17

What are diastereomers?

Answer 17

Stereoisomers that are not perfect mirror of each other

Question 18

What are epimeres?

Answer 18

Diastereomeres that differ in the configuration of exactly 1 chiral center

Question 19

What type of stereoisomers is this?

Answer 19

Enantiomers

Question 20

Is this a chiral or an achiral compound?

Answer 20

Achiral compound

→ b/c they are symmetrical

Question 21

What are geometric isomers?

Answer 21

Stereoisomerism that results from restricted rotation about chemical bonds

1. Is sometimes possible when a ring is present
2. Is sometimes possible when a double bond is present

Question 22

How are the different groups sorted when presenting in cis-trans isomers?

Answer 22

By atomic number

Question 23

What are trans-isomers?

Answer 23

Isomers with 2 identical groups closed to each other

Question 24

What is conformational isomerism?

Answer 24

Spacial structure of atoms that are directly not connected to each other

Question 25

2 types of H atoms in conformational isomer

Answer 25

1. Axial H-atoms: are above / below the level of the ring 2. Equatorial H-atoms: are in the level of the ring

Question 26

2 types of conformation of cyclohexane

Answer 26

Boat and chair conformation

Question 27

Which conformation type of **cyclohexane** is more favorable? Why?

Answer 27

* Chair conformation → more stable → is more favorable * Boat conformation is less favorable → H-atoms are close to each other → unstable

Question 28

2 types of **conformation** based on Newman-projection

Answer 28

Staggered and eclipsed conformation

Question 29

Describe **staggered conformation**

Answer 29

* Geometric isomer * Staggered conformation is the arrangement of atoms or groups of atoms in a molecule resulting in a 60^o dihedral angle

Question 30

Describe **eclipsed conformation**

Answer 30

* Geometric isomer * **Two atoms and/or groups whose dihedral angle is 0^o**. In other words, their bonds to the axis of rotation are aligned * → less **STABLE**

Question 31

What are the 4 characteristics of conformational isomer (Newman's projection)?

Answer 31

1. Anti 2. Syn 3. Periplanar 4. Clinal

Question 32

What does anti mean in conformational isomer (Newman's projection)?

Answer 32

The substituents have the maximal distance from each other → energetically favorable

Question 33

What does syn mean in conformational isomer (Newman's projection)?

Answer 33

The substituents have the minimum distance from each other → require more energy

Question 34

What does periplanar mean?

Answer 34

the covalent bonds are parallel to each

Question 35

What does clinal mean?

Answer 35

covalent bonds are not in the same plane

Question 36

What type of conformation is this?

Answer 36

Anti, periplanar

Question 37

What type of conformation is this?

Answer 37

Syn, clinal

Question 38

What type of conformation is this?

Answer 38

Anti, clinal

Question 39

What type of conformation is this?

Answer 39

Syn, periplanar

Question 40

What are the 2 type of conformation of nucleoside?

Answer 40

Anti Syn

Question 41

Describe the anti form of nucleoside?

Answer 41

Base is rotated away from the ribose

Question 42

Describe the syn form of nucleoside?

Answer 42

Base is in proximity, right above the ribose !!! Pyrimidines cannot be in this conformation because oxygen will be too close to each other