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ADV Chemistry- Organic > Organic Chemistry and instrumental analysis > Flashcards

Organic Chemistry and instrumental analysis Flashcards

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1
Q

There are two ways in which a bond can be broken. Name them.

A

Homolytic fission and heterolytic fission

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2
Q

Describe homolytic fission.

A

Occurs when each atom retains 1 electron from the covalent bond and the bond breaks evenly, resulting in the formation of 2 neutral radicals.

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3
Q

What type of bond will be broken homolytically?

A

Non polar covalent bond

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4
Q

Describe heteolytic fission.

A

Occurs when 1 atom retains both electrons from the covalent bond and the bond breaks unevenly,

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5
Q

What type of bond will be broken heterolytically?

A
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6
Q

What does a single headed arrow and a double headed arrow indicate?

A

A single headed arrow indicates the movement of a single electron.
A double headed arrow indicates the movement of an electron pair.

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7
Q

What does the tail of an arrow show?

A

The tail of the arrow shows the source of the electron(s).

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8
Q

What does the head of the arrow indicate?

A

The head of the arrow indicates the destination of the electron(s).

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9
Q

What do 2 single headed arrows starting at the middle of a covalent bond indicate?

A

Two single headed arrows starting at the middle of a covalent bond indicate homolytic bond fission is occurring.

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10
Q

What does a double headed arrow starting at the middle of a covalent bond indicate?

A

A double headed arrow startling at the middle of a covalent bond indicates hetelytic bond fission is occurring.

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11
Q

What does an arrow draw with the head pointing to the space between two atoms indicate?

A

An arrow drawn with the head pointing to the space between two atoms indicates that a covalent bond will be formed between those two atoms.

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12
Q

What are nucleophiles?

A

Nucleophiles are negatively charged ions or neutral molecules that are electron rich, they are attracted towards atoms bearing a partial or full positive charge and are capable of donating an electron pai to form a new covalent bond.

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13
Q

Give examples of nucleophiles.

A

Carbanions(C-), Cl-, OH-, H2O, Br-, CN-, NH3.

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14
Q

What are electrophiles?

A

Electrophiles are positively charged ions or neutral molecules that are electron deficient, they are attracted towards atoms bearing a partial or full negative charge and are capable of accepting an electron pair to form a new covalent bond.

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15
Q

Give examples of electrophiles.

A

Carbocations (C+), H+, NO2 (+).

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16
Q

What is an addition reaction?

A

Molecule added across a C=C or C to C triple bond.
C2H4 +Br2 forms C2H4Br2

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17
Q

What is an elimination reaction?

A

Removal of a molecule leaving behind a C=C double bond.
C2H5OH forms C2H4 + H2O
Remember: a molecule is removed not an atom.

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18
Q

What is a condensation reaction?

A

Two molecules join together and a small molecule is removed.
CH3OH + CH3COOH forms CH3OCOCH3 + H2O
(Methanol + Ethanoic acid)

19
Q

What is a hydrolysis reaction?

A

Molecule splits into two molecules with the addition of a small molecule being added.
CH3OCOCH3 + H2O forms CH3OH + CH3COOH.
The small molecule added is water (H2O)

20
Q

What is a substitution reaction?

A
21
Q

What is an oxidation reaction?

A
22
Q

What is haloalkanes?

A

Haloalkanes (alkyl halides) are substituted alkanes in which one or more of the hydrogen atoms is replaced with a halogen atom.

23
Q

What is a primary monohaloalkane?

A

Carbon bonded to the halogen group is bonded to 1 other carbon. RCH2-X

24
Q

What is a secondary haloalkane?

A

Carbon bonded to the halogen is bonded to 2 other carbons. (R)2CH-X

25
Q

What is a tertiary haloalkane?

A

Carbon bonded to the halogen is bonded to 3 other carbon. (R)3C-X

26
Q

What type of reactions do monohaloalkanes take part in?

A

Elimination reactions with a strong base such as potassium or sodium hydroxide in ethanol to form alkenes.

Nucleophilic substitution reactions with:
- aqueous alkalis to form alcohols
- alcoholic alkoxides to form ethers
- ethanolic cyanide to form nitriles, which can be hydrolysed to form carboxylic acid.

27
Q

Which type of monohaloalkane is used in the SN1 mechanism?

A

Tertiary haloalkanes

28
Q

Why are tertiary haloalkanes used in SN1?

A

Tertiary haloalkane used because the alkyl groups are said to have an inductive effect which stabilises the C+ by donating electrons.

29
Q

Which haloalkanes are used for SN2 mechanism?

A

Primary or secondary haloalkanes.

30
Q

Why are tertiary haloalkane not used in SN2 mechanism?

A

Because of steric hinderance. If a tertiary haloalkane is used than a nucleophilic attack towards the carbon atom from the side opposite of the halogen is not possible, because of the 3 bulky alkyl groups will limit access to the C+ atom.

31
Q

What is formed when a primary alcohol is oxidised?

A

Aldehydes are formed when primary alcohols are oxidised and aldehydes can be furthered oxidised to carboxylic acids using:
- Acidified potassium dichromate solution ( turns from orange to green)
- Fehling’s solution (turns from blue to brick red)
- Tollen’s reagent (turns from colourless to silver mirror effect)

32
Q

What reagents are used to oxidise primary alcohols into aldehydes?

A

Oxidising agents are used to oxidise primary alcohols, such as acidified potassium dichromate solution (turns from orange to green) or copper (II) oxide (from black to red)

33
Q

How are ketones formed?

A

Ketones are formed when secondary alcohols are oxidised.

34
Q

How are esters formed?

A

When alcohols reacts with carboxylic acids. This is a condensation reaction in which sulfuric acid is used as a catalyst to provide H+ ions.

35
Q

How can alcohols be prepared?

A
  • haloalkanes by substitution, using aqueous alkali, such as sodium or potassium hydroxide in ethanol (either SN1 or SN2)
  • Reduction of aldehydes and ketones using lithium aluminium hydride (LiAIH4) dissolves in ether.
  • Hydration of alkenes using phosphoric acid as a catalyst
36
Q

What do alcohols react with?

A

-Alcohols react with reactive metals such as sodium and potassium to form alkoxides.
- Alcohols can react with acid chlorides to form esters, as they react with carboxylic acids. This is a 2 way process:
Stage 1- the acid is converted into an acid chloride by reaction with either thionyl chloride (SOCl2), phosphorus (V) chloride (PCl5) or phosphorus (lll) chloride (PCl3)
Stage 2-the acid chloride formed reacts with an alcohol to form esters.
- Dehydration to form alkenes using aluminium oxide, concentrated sulphuric acid or concentrated phosphoric acid.
- formation of esters by reaction with carboxylic acids using concentrated sulphuric acid as a catalysts.
- oxidation of primary alcohols to form aldehydes and then carboxylic acids and secondary alcohols to from ketones, using acidified permanganate, acidified dichromate or hot copper (ll) oxide.

37
Q

What type of bonding is present in alcohols?

A

Hydrogen bonding due the hydroxyl group that makes the alcohol polar. This gives alcohol high bp and mp.

38
Q

What is the functional group of ethers?

A

Functional group (alkoxy group) is -OR, and have a general structure R’-O-R”. R’ and R” are alkyl group.

39
Q

How are ethers formed?

A

Ethers are formed in a nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide.

40
Q

Why do ethers have low boiling points?

A

Due to the lack of hydrogen bonding between ether molecules, they have lower boiling points than the corresponding isomeric alcohols.

41
Q

Are ethers soluble in water?

A

Larger ethers are insoluble in water due to their increased molecular size, however methoxymethane and methoxyethane are soluble in water.

42
Q

Why ethers are used as solvents?

A

Because they are relatively inert chemically and will dissolve many organic compounds.

43
Q
A

ADV Chemistry- Organic (1 decks)

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