Organic chemistry 2

Question 1

언제 Chemical Reactions 라고 하나 [3]

Answer 1

1. When chemical changes in matter resulting in new substances.
2. When old bonds are broken and new ones are created.
3. When rearrangement and exchange of atoms to produce new molecules

Question 2

Reaction Mechanism

Answer 2

The reaction mechanism describes the sequence of elementary reactions that must occur to go from reactants to products.
It describes the reactants and intermediates involved and products formed.

Question 3

Bond Fission(bond breakage) 과정

Answer 3

1. a covalent bond is formed when electrons are shared between two atoms in the classical sense.
2. a single bond (sigma bond) is thus made up of two electrons.
3. a chemical reaction takes place when old bonds are broken and new ones are formed.
4. the breakage of a chemical bond is often referred to as bond fission

Question 4

Bond Fission 2가지 종류

Answer 4

1. homolytic bond fission
   a type of bond fission that involves the dissociation of a molecule where one electron is retained by each of the original fragments of the molecule. Therefore, when a neutrally charged molecule is subjected to homolytic fission, two free radicals are obtained as the product (since each of the chemical species retains one electron from the bond pair).
2. Heterolytic bond fission
   a type of bond fission in which a covalent bond between two chemical species is broken in an unequal manner, resulting in the bond pair of electrons being retained by one of the chemical species (while the other species does not retain any of the electrons from the bond pair). When a neutrally charged molecule undergoes heterolytic fission, one of the products will have a positive charge whereas the other product will have a negative charge.

Question 5

free radical

Answer 5

a species which can contain an unpaired electron in their atomic orbital and can exist independently

Question 6

curly arrow 주의점 (lone pair of e- 경우) - making a new bond

Answer 6

movement of an electron or two electrons(molecular orbital). This does not show the movement of atoms.
start from a lone pair of e- and end the arrow near the atom to get bonded between.

• 추가로 to transfer a lone pair of e- 가 bond 만드는 방법 중 하나지만, some of them 불가, 왜냐하면 결합 가능 수 초과안되기 때문.

Question 7

curly arrow 주의점 (breaking a single bond)

Answer 7

to take 2 electrons in the bond then place them on the more electronegative atom.

double-headed curly arrow starts from bond and end the arrow near the more electronegative atom

Question 8

Leaving group

Answer 8

an atom or a group of atoms which breaks away from the rest of the molecule, taking with it the electron pair which used to be the bond between the leaving group and the rest of the molecule. The bond scission(분리) occurs via heterolytic bond fission

Question 9

chain reaction

Answer 9

The mechanism of free radical substitution of alkanes involves a chain reaction.

A reaction whose mechanism includes one or more steps that are repeated indefinitely, until the chain is terminated, or reactants are used up.

The products of a chain reaction contribute to the reactants of another reaction

Question 10

electrophiles (+)

Answer 10

electron deficient, could hold more negative charge
tend to gain pairs of electrons (accept electrons)
positively charged ions (cations) or neutral molecules

Fx) proton, carbocation, aluminium chloride, hydrodium ion, ammunium ion, carbonyl, c+electronegative

Question 11

nucleophiles (-)

Answer 11

electron rich, could carry excess negative charge
tend to donate electron pairs to another atom
negatively charged ions (anions) or neutral molecules
Fx) 많음. double bond, OH, F, I, Br, Cl, NH3, H2O, CH3O, CH3S …..

Question 12

Markovnikov Rule (when stable정의 및 분류 2가지)

Answer 12

1. one rule states that with the addition of a HX(halogen) to an asymmetric alkene, the acid hydrogen (H) gets attached to the carbon with more hydrogen substituents and the halide (X) group gets attached to the carbon with more alkyl substituents.
2. . The addition of the hydrogen ion to one carbon atom in the alkene creates a positive charge on the other carbon, forming a carbocation intermediate. The more substituted the carbocation, the more stable it is.

Question 13

Benzene (aromatic compounds)

Answer 13

1. hydrocarbon
2. aromatic compounds are called aromatic as when these benzene containing compounds where firstly isolated from natural sources they had a pleasant smell
3. molecular formula : C6H6

Question 14

Tollen’s Reagent/ Silver Mirror Test

Answer 14

Tollen’s reagent is used to distinguish an aldehyde from a ketone. Aldehydes can be further oxidised to carboxylic acids, but ketones cannot. Tollens’ reagent is a weak oxidising agent containing silver nitrate in ammonia. When warmed with Tollens reagent, the aldehyde is oxidised to a carboxylic acid, and the silver ions in solution are reduced to silver metal.
A “silver mirror” is formed on the walls of the test tube (or sometimes just a silver-grey solid is formed).

Question 15

Fehling’s reagent

Answer 15

blue solution used to differentiate between water an aldehyde and a ketone. The substance to be tested is heated together with Fehling’s solution; a red precipitate indicates the presence of an aldehyde. Ketones (except alpha hydroxy ketones) do not react.

Question 16

2,4-dinitophenylhydrazine/ Brady’s Reagent

Answer 16

Brady’s Reagent is a solution of 2,4-dinitrophenylhydrazine (2,4-DNP or 2,4-DNPH) in methanol and sulphuric acid (i.e. acidified solution). Brady’s Reagent is a clear, green solution.
Aldehydes and ketones react with 2,4-dinitrophenylhydrazine (2,4-DNP or 2,4-DNPH) to form an orange or yellow precipitate.
No precipitate is formed with other carbonyl compounds such as carboxylic acids or esters.

Question 17

If an aldehyde or ketones needs to be identified:

Answer 17

The orange/yellow solid substance must be purified by recrystallisation
Melting point must be determined
Melting point is compared to a database of published melting points for these derivatives e.g.:
heptan-2-one b.p. = 151°C; m.p of 2,4-DNP derivative = 90°C
octan-2-one b.p. = 173°C; m.p of 2,4-DNP derivative = 58°C

Question 18

Uses of Esters

Answer 18

perfumes, fruit flavourings, cosmetics

Esters are used as an organic solvent.
Polyesters are used to make plastics.

Question 19

nucleophilic addition (aldehyde/ketone&raquo_space;hydrogen/cyanide» hydroxynitrile)

Answer 19

The reaction isn’t normally done using hydrogen cyanide itself, because this is an extremely poisonous gas. Instead, the aldehyde or ketone is mixed with a solution of sodium or potassium cyanide in water to which a little sulphuric acid has been added. The pH of the solution is adjusted to about 4 - 5, because this gives the fastest reaction.