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CHM 121 2023/2024 > Hydrocarbons > Flashcards

Hydrocarbons Flashcards

1
Q

Two compounds that have the same molecular formula, but differ in the order in which the atoms are bounded, are called?

A

Structural isomers

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2
Q
  1. Alkanes are gases when they have _____ to _____ carbon atoms
  2. They are liquids when they have ______ to ______ carbon atoms
  3. They are solid when they have _____ to _____ carbon atoms?
A

1-4 carbon atoms
5-8
9-17

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3
Q

Alkanes are soluble in water
True/False

A

False. Alkanes are insoluble in water i.e they are non-polar
And they have a density of 0.62g/ml - 0.79g/ml)

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4
Q

Branching reduces boiling and melting point
True/false

A

True

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5
Q
  1. The process by which hydrogen atoms are replaced by halogen atoms, involving free radical production is called?
  2. How many reactions are involved in the chain reaction? Name them?
A
  1. Chain reaction
  2. 3 ; (a) initiation reaction : lone pair is on the right
    (b) Propagation reaction : lone pair is on both left and right
    (c) Termination reaction : lone pair is at the left
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6
Q

Which step of radical chain mechanism requires outside energy?
What can be used as this energy?

A
  1. Initiation reaction
  2. UV light is used as the energy
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7
Q
  1. Why are alkenes more reactive than alkanes?
A

Because pi bonds are weaker than Sigma bond
OR
Higher energy is needed to break π bond and higher electron density in pi bonds

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8
Q
  1. Under what condition could ozonolysis of an alkene give only one product?
  2. What is used for the test of unsaturation in alkene?
  3. Addition of HBr to propene gives two isomeric brominated compounds
    True/False
A
  1. Symmetrical
  2. Bromine water. If the reddish brown is disappears then the hydrocarbon is Alkene
  3. True
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9
Q

The addition of unsymmetrical reagents to unsymmetrical alkenes occur in such away that the negative part of the addendum goes to the carbon atoms of double bond which carries less number of hydrogen atom is called by?

A

Markovnikoff rule

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10
Q

What year was markovnikoff rule formulated?
And by who?

A

The Russian chemist Vladimir Vasilyevich Markovnikoff in 1865

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11
Q

If HCl adds to an unsymmetrical alkene like propene what will the major product be?

A

2-Chloropropane

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12
Q

Hydration of internal alkynes leads to formation?

A

Ketones

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13
Q

Alkenes produces alkanes through what reaction?

A

Hydrogenation reaction

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14
Q

________ and _______ are used to test if an organic compound is saturated or unsaturated

A

Bromine & kMnO4

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15
Q

What are the two ways in which alkenes can be produced?

A

A. From Halogenation - Elimination
2. Reagent - Alcoholic sodium or potassium hydroxide
3. Conditions - Reflux in alcoholic solution

B. From Alcohols - Dehydration
Reagent: Conc sulphuric acid or conc phosphoric acid
Conditions: Reflux/170°C

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16
Q

Ethene is collected over what
And why?

A

Water
Ethene is collected over water because it has low solubility in water, making it easy to capture and measure.

17
Q

When Ethanol is heated with excess of concentrated sulphuric acid. The gases produced are passed through sodium hydroxide solution why?

A

To remove the carbon dioxide and sulphur dioxide produced from side reactions

18
Q
  1. Alkynes have a length of what?
  2. The most important commercial alkyne is?
A
  1. 1.20A°
  2. Acetylene which is used as fuel
19
Q

1.The the triple bond is between 2 carbon atoms, the alkyne is_______?

  1. If the triple bond is flanked by a hydrogen and carbon, the alkyne is ________,?
A

Internal
Terminal

20
Q

Terminal alkynes are more stable than internal alkynes
True/False

A

False
Internal alkynes are more stable than terminal alkynes

N.B: pka of alkane = 50
pka of alkene= 45
pka of alkyne= 25

21
Q
  1. When terminal alkynes are deprotonated by very strong bases, what’s the resulting anion called?
  2. Deprotonation of terminal alkynes is commonly done with?
A
  1. An Acetylide ion
  2. NH2, in the form of NaNH2(sodium amide or sodamide
22
Q

What’s lindlar catalyst used for?

A

The lindlar catalyst is used to catalyze the hydrogenation of alkynes to alkenes, but not that of alkenes to alkynes

23
Q

What reaction forms cis alkenes and trans alkenes?

A

The reaction between alkyne and lindlar catalyst gives cis alkenes

The reaction between alkyne and sodium in liquid ammonia gives trans alkenes

Alkyne + lindlar catalyst = Cis alkenes
Alkyne + Sodium in liquid ammonia = transalkenes

24
Q
  1. Silver(I) and copper(I) salts reacts with terminal alkynes to form what
  2. Why do internal alkynes not react and form a precipitate?
A

Silver and copper Acetylide

Because they don’t have acidic proton

25
Q
  1. Ethyne is prepared by the reaction between what and what?
  2. Ethyne is normally prepared by what?
A
  1. Reaction between calcium carbide with water
  2. Pyrolysis of methane
26
Q

What are the chemical test that distinguishes between alkenes and alkynes

A
  1. Alkynes react with ammoniacal silver nitrate, and it gives a white ppt whereas alkenes do not
  2. Alkynes react with ammoniacal cuprous chloride to form a blue to red colour while alkenes do not
27
Q

Hydration of terminal alkynes yield?
Hydration of internal alkynes yield?

A

Aldehyde
Ketones

28
Q

Deprotonation of terminal alkynes is commonly done with? In the form of what?

A

-NH2 in the form of NaNH2(sodium amide or sodamide)

29
Q
  1. When trialkenylborane is treated with alkaline hydrogen peroxide it forms what?
  2. What is used to stop hydroboration of terminal alkynes at the first step?
A
  1. An enol. The enol eventually converts into a stable carbonyl product via Reto - enol tautomerism
  2. Bulky distributed boranes(R2BH) such as disamyl borane and 9-BBN instead of BH3
30
Q

Ammonical Cuprous chloride on reacting with Ethyne gives what?

A

Gives copper Acetylide or cuprous and ammonium chloride. The ammonical Cuprous chloride changes from blue to red on reacting with Ethyne. But there’s no colour change when it reacts with ethene

31
Q
  1. Grignards reagents is also called?
A

Alkyl magnesium halides

32
Q
  1. The reaction
A
33
Q

Ozonolysis of alkenes give what?

A

Alcohols, alkanals, ketones, carboxylic acids

CHM 121 2023/2024 (3 decks)

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