Mod 7.3 - Products of Reactions Involving Hydrocarbons Flashcards
What type of reaction is a hydrogenation reaction?
It is an addition reaction. It refers when hydrogen molecules are used to saturate organic compounds (essentially breaking down triple and double bonds)
What is the difference between cis and trans alkenes?
Cis alkenes - at the double bond site, the hydrogens attached to the two carbons are on the same side
Meanwhile, trans alkenes - at the double bond site, the hydrogens attached to the two carbons are on opposite sides
What occurs when an alkyne reacts with hydrogen gas (excess H2) and a metal catalyst)?
A cis-alkene is formed. Where there was a triple bond, it is replaced by a double bond which is cis.
What are the different hydrogenation reactions? (3)
Hydrogen gas with a metal catalyst (alkyne and alkene)
Hydrogen gas with a poison catalyst (also referred to as Lindlar’s catalyst)
Dissolving a Group 1 metal in cold liquid ammonia
What are the different hydrogenation reactions? (3)
Hydrogen gas with a metal catalyst
Hydrogen gas with a poison catalyst (also referred to as Lindlar’s catalyst)
Dissolving a Group 1 metal in cold liquid ammonia
What are the different hydrogenation reactions? (3)
Hydrogen gas with a metal catalyst
Hydrogen gas with a poison catalyst (also referred to as Lindlar’s catalyst)
Dissolving a Group 1 metal in cold liquid ammonia
What occurs when an alkene reacts with hydrogen gas with a metal catalyst
Forms an alkane - replace the double bond with a single bond, and place hydrogens around the carbons
What occurs when an alkene reacts with hydrogen gas and a poison catalyst (Lindlar’s Catalyst)?
It has the same affect as an alkene reacting with hydrogen gas and metal catalyst –> it forms an alkane (with the double bond broken)
What occurs when a Group 1 metal is dissolved in cold liquid ammonia?
This catalytic process results in a trans alkene (the Hydrogens attached to the double bond is on opposite ends)
What is halogenation?
It is an addition reaction. Halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound.
What are saturated vs unsaturated bonds?
Saturated - these are unreactive and only have single bonds
Unsaturated - They are reactive and have double or triple bonds
For halogenation, what are the two halogens normally used? Why not the others?
Normally use Br2 and I2. We DONT use F2 and Cl2 because they are extremely reactive and can’t be controlled.
What is the reaction of a halogenation reaction?
Alkyne + excess halogen –> trans alkene –> haloalkene
What occurs when an alkyne reacts with excess halogens (either bromine or iodine)?
Forms a trans alkene with the halogens, and stops if there is NO excess halogens, but if there is excess halogens –> haloalkene
What are hydrogen halides?
These have one hydrogen and one halogen such as HF, HCL, HBr and HI
What is the reactivity order of hydrogen halides?
HI > HBr > HCl > HF
What is Markovnikov’s rule?
The hydrogen adds to the carbon with the greatest number of hydrogens, the halogen adds to the carbon with the fewest hydrogens
For what is Markovnikov’s rule applied?
Used for Hydrogen halide reactions with an alkyne
What are the different reaction types for hydrogen halides?
Addition to an internal alkyne
Addition to a terminal Alkyne
What occurs when an alkyne (internal) reacts with a hydrogen halide?
It will break the triple bond into a double bond, and then using Markovnikov’s rule, the hydrogen will attach to the carbon with the greatest number of hydrogens, and the halogen adds to the carbon with the fewest hydrogens. In some cases, this may produce 2 different products, especially as the halogen can fall on either carbon on the double bond (if both carbons have same number of hydrogens)
If it reacts with excess hydrogen halide, the reaction will continue to break apart the double bond into a single bond, forming an haloalkane, where the Markovnikov’s rule is applied again, and halogens attach to the carbon with the least hydrogens (typically the carbon which got the halogen in the previous step), and then the hydrogen adds to the carbon with the most carbons
What occurs when an alkyne (terminal) reacts with a hydrogen halide?
When HX is added to a terminal alkyne, the X adds to the second carbon rather than the first, because the first carbon has more hydrogens attached to it already (according to Markovnikov’s rule)
What are hydration reactions?
A hydration reaction is a chemical reaction in which a substance combines with water.
What are the different hydration reactions (involving water (H2O))?
Reactions involving alkynes and water
Reactions involving alkenes and water
Oxidation of alkanols to aldehydes, carboxylic acids or ketones
Dehydration of alkanols to alkenes using heat and concentrated H2SO4
What is required for a reaction involving alkynes and water?
It involves a dilute acid (typically represented by H+ above the arrow, as well as a heavy metal ion such as Hg+ (typically mercury ion))
What occurs when an alkyne reacts with water?
When water undergoes addition with non-terminal alkynes, a ketone is formed (double bond O)
(In the presence of a dilute acid and a heavy metal ion such as Hg+)
What is required for a reaction involving alkenes and water?
Requires dilute sulfuric acid (written above arrow)
What occurs when an alkene reacts with water?
Alkene = water –> alcohol
The hydroxyl group can be on either side of the bond that was the double bond (thus typically having 2 different possible products)
(In the presence of dilute H2SO4)
What is required for a reaction involving alkanols to aldehydes, carboxylic acids or ketones?
Requires Potassium permanganate (KMnO4) and sulfuric acid (typically written above the arrow; KMnO4/H2SO4)
What is the reaction invovling alkanols to aldehydes/carboxylic acids/ketones called?
It is called an oxidation reaction
What are the different types of oxidation reactions that can occur depending on the property of the alkanol?
Primary Alkanols
Secondary Alkanols
Tertiary alkanols
What are primary, secondary and tertiary alkanols?
A primary alcohol has the OH bonded to a carbon which is bonded to one carbon
A secondary alcohol has the OH bonded to a carbon which is bonded to two carbons
A tertiary alcohol has the OH bonded to a carbon which is bonded to three carbons
What occurs when a primary alkanol reacts with KMnO4/H2SO4?
It forms an aldehyde, before forming a carboxylic acid group
WHat occurs when a secondary alkanol reacts with KMnO4/H2SO4?
It forms a ketone where the OH was
What occurs when a tertiary alkanol reacts with KMnO4/H2SO4?
It has no reaction
What is dehydration reaction?
A dehydration reaction is a chemical reaction in which the reactant loses two hydrogen atoms and an oxygen atom, which then form a water
What does a dehydration reaction require to continue?
Needs an alkanol to be heated with concentrated H2SO4 (typically indicated above the arrow)
What are the two different types of dehydration reactions which may occur?
Primary alkanol dehydration
Secondary alkanol dehydration
Tertiary alkanol dehydration
What occurs if a primary alkanol is exposed to conc H2SO4 and heat?
It will form a double bond at the end of the chain, and produce water (this water is lost) (terminal alkene)
i.e. Pentan-1-ol –> pent-1-ene + H2O
What occurs if a secondary alkanol is exposed to conc H2SO4 and heat?
It will form a double bond
What occurs if a tertiary alkanol is exposed to conc H2SO4 and heat?
It becomes a NON terminal alkene (even if originally the OH was on the second carbon)
What is a substitution reaction?
A substitution reaction is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group
What is required for a halogen substitution reaction?
It requires u.v light
What occurs when an alkane is reacting with a halogen (Cl or Br) and is exposed to u.v. light?
It substitutes a hydrogen from the alkane with the halogen and also forms a hydrogen halide.
For example;
pentane + Br2 –> 1-bromopentane + HBr
NOTE: IF THE HALOGEN IS CONSTANTLY PROVIDED, IT WOULD CONSTANTLY ADD ON THE MOLECULE, UNTIL IT IS FILLED WITH THE HALOGEN
