Organic Nomenclature

Question 1

Polycyclic:

Answer 1

Question 2

Heterocycle:

Answer 2

Question 3

Aromatics with heteroatoms (heteroaromatic):

Answer 3

Question 4

Aromatic hydrocarbon (delocalised electrons):

Answer 4

Question 5

What is a Thiol?

Answer 5

Organosulfur compound of the from R-SH, where R represents and alkyl or any other organic substituent.

Question 6

What is an Ether? (3)

Answer 6

• Two hydrocarbon groups bonded to one oxygen.
• Can be formed from alcohol condensation reactions.
• Oxygen makes the molecule polar.

Question 7

What is a Thioether? (2)

Answer 7

• Thiol group, where the Sulfur is not attached to the end of the hydrocarbon chain, but instead located between two alkyl groups.
  -i.e. C-S-C configuration.

Question 8

What is a Haloalkane/ Alkyl Halide?

Answer 8

Organic molecules derived from alkanes that contain one
or more Halogen atoms (Br, I,F, Cl).

Question 9

What is an Amide?

Answer 9

Contains a functional group derived from carboxylic acid, with NRR’, Nh2, or NHR group replacing the OH of the acid.

Question 10

What is an Amine? (2)

Answer 10

• Functional group is an ammonia molecule, where one hydrogen is replaced by an alkyl group.
• Most common organic bases.

Question 11

What is an Aldehyde?

Answer 11

Contains the carbonyl group (C=O), with at least 1 hydrogen attached (i.g. -CHO group).

Question 12

What is an aromatic ring?

Answer 12

Pi bonds are delocalised in the ring.

Question 13

What is a carboxylic acid? (2)

Answer 13

• Contains the COOH (carboxyl) functional group.
• Forms weak acids that are widely distributed in nature, especially citrus fruits

Question 14

What is an ester? (2)

Answer 14

• An ester is a compound where the H atom of the carboxylic acid is replaced by a carbon-containing group.
• Esters are responsible for many of the flavors and fragrances in fruits and flowers. By changing the chain length, we can experience different smells.

Question 15

What is a ketone? (2)

Answer 15

• Ketone also contains the carbonyl group, but the interior of the molecule.
• Less reactive than aldehydes, and are used widely as solvents.

Question 16

What are isomers?

Answer 16

Isomers are compounds which have the same atomic composition and molecular formulae, but differ in the way the atoms are arranged, and therefore the physical and chemical properties, which leads to structural diversity and a vast number of compounds.

Question 17

What are the types of isomers?

Answer 17

Question 18

What are structural isomers? (2)

Answer 18

Structural (constitutional) isomers: same atomic composition (molecular formula) with different sequential arrangements.
a. Different connectivity between atoms.
b. Different physical properties (and in some cases chemical properties).

Question 19

What are stereoisomers? (2)

Answer 19

• Stereo isomer: same bonding sequence of atoms, i.e.
  same condensed formula; but different orientation
  of atoms in space. The shape is important, we often need to use 3D projection formulae, to represent the molecule.

a. Stereoisomerism is very important in biology.
b. e.g. an enzyme, which is substrate specific at
its binding site can have different types of
binding depending on the conformation of the
molecule.

Question 20

Staggered vs Eclipsed: (2)

Answer 20

a. Staggered: gives rise to a phenomenon, where the H atoms are arranged in an alternating manner between the different carbons; has a lower energy.

b. Eclipsed: H atoms are arranged so as to face the same direction as the different Carbon atoms; has a higher energy and experience torsional strength (increased potential energy due to electron-electron repulsion).

Question 21

What is a steric hindrance?

Answer 21

Steric hindrance: when two bulky groups are close to each other/repulsive interaction between two big substituents in close proximity. The lowest energy conformation is the most stable, whereas the higher
energy conformation is not thermodynamically stable.

Question 22

What are stereo isomers in cyclic hydrocarbons? (2)

Answer 22

1.) Chair isomer: resembles a chair, lowest energy conformation; all hydrogen atoms are staggered,
lowering steric and torsional strain.

2.) Boat conformation: (ring flip) no bonds are broken, atoms are rearranged; atoms can eclipse each other, resulting in steric and tortional strain.

Question 23

What are geometric isomers? (3)

Answer 23

Geometric: not the same molecule, which have different physical properties, but similar chemical properties

a. require a rigid unit (pi bond or a ring) about which rotation is not possible.

b. Interconversion of isomers require bond
breaking which needs a lot of energy.

c. e.g. alkanes have no rigid bonds, and no geometric isomers possible, but alkenes have a c=c double bond, which gives the rigidity needed for a geometric isomer.

Question 24

Two types of geometric isomers:

Answer 24

i. Cis isomer: on the same side (Z). Cis isomer has higher energy (due to steric hindrance and torsional strain, as the electron clouds of the atoms are in close proximity, and e- repulsion is greater).

ii. Trans isomers: on opposite sides (E). Trans isomer: most stable orientation, since bulky groups are further away, and the structure is more stable.

Question 25

What is a Cahn Ingold Prelog sequence rule?

Answer 25

Cahn Ingold Prelog sequence: determine the priority of a stereoisomer of a molecule, and assign an R or S descriptor each stereocenter and an E or Z descriptor to each double bond so that the configuration of the entire molecule can be specified uniquely by including the descriptors in its systematic name.

Question 26

What are the rules for geometric isomers? (4)

Answer 26

1.) Compare the atomic number (Z) of the atoms directly attached to the stereocenter; the group having the atom of a higher atomic number receives higher priority. 2.) If there is a tie, we must consider the atoms at distance from the stereocenter. Each list is arranged in order of decreasing atomic number. Then the lists are compared atom by atom; at the earliest difference, the group containing the atom of higher atomic number receives higher priority. 3.) This process is repeated recursively, each time with atoms one bond farther from the stereocenter until the tie is broken. 4.) For alkenes and similar double-bonded molecules, the same prioritizing process is followed for the substituents. In this case, it is the placing of the two highest priority substituents with respect to the double bond which matters. If both high-priority substituents are on the same side of the double bond, i.e. in the cis configuration, then the stereoisomer is assigned a Z (zusammen) . If by contrast they are in a trans configuration, then the stereoisomer is assigned an E (entgegen).

Question 27

Cycloalkanes: have less _____ than their open chain counterparts and movement is greatly reduced; positions which the substituents occupy, could give rise to different _____isomers.

Answer 27

flexibility geometric

Question 28

What is an Enantiomers?

Answer 28

Enantiomers: chiral (handed) compounds.

Question 29

What is a chiral molecule? (5)

Answer 29

1.) A molecule is called chiral, if it cannot be superimposed on its mirror image by any combination of rotations, translations and some conformational changes. 2.) A molecule that exists as a pair of non-superimposable mirror images is called chiral. 3.) Molecules with one stereogenic centre exist as a pair of enantiomers. 4.) The molecule cannot be planar, and cannot have an angle of symmetry. 5.) Compounds containing carbon atoms with four different attached groups are inherently chiral.

Question 30

e.g. ibuprofen has __ stereogenic centre:

Answer 30

one

Question 31

e.g. some _____ have multiple stereogenic centres:

Answer 31

multiple

Question 32

A molecule with n stereogenic centres can give rise to a maximum of ___ stereoisomers.

Answer 32

n^2 e.g. cholesterol has 8 stereogenic centres and therefore 2^8 or 256 possible stereoisomers.

Question 33

What type of carbon is needed for an enantiomer?

Answer 33

Require a saturated sp3 hybridised carbon (4 different substituents). A carbon atom attached to four different atoms or groups is called a stereogenic centre, a chiral carbon, or an asymmetric carbon.

Question 34

Enantiomer molecules are _____-______ (cannot lay them on top of each other), but are mirror images of each other. They have virtually the same chemical properties. Physical properties are identical, except that they interact with plane polarised light differently. They have optical activity and are known as _____ isomers. They can rotate light to the right (dextrorotatory or +) or left (Laevorotatory or -). Organic chemists use the labels ___ and ___ to distinguish the two forms.

Answer 34

non-superimposable optical R S

Question 35

What is a Racemic mixture?

Answer 35

Racemic mixture: A mixture of 50% (+) and 50% (-); the mixture is optically inactive, but the individual molecules are still optically active Racemate: a drug that occurs as a mixture of a compound with different stereogenic centres. Thalidomide was sold as racemate without proper testing, and one enantiomer of the compound was harmful to developing embryos.