Topic 4A - Part 2 Flashcards
Fill in the gaps
Reactions can be classified according to … … to the … during the reaciton and what the … … are.
Reactions can be classified according to what happens to the reactants during the reaction and what the end products are.
Define Addition
the reactants combine to form a single product.
Define substitution
One functional group is replaced by a different functional group.
define polymerisation
A reaction in which many small molecules, known as monomers, join together to form a long, repeating molecule called a polymer.
Define free radicals
A free radical is an atom, molecule, or ion that has an unpaired electron in its outermost shell. This makes it highly reactive because it seeks to pair up the unpaired electron by reacting with other atoms or molecules.
Free radicals play a role in both beneficial processes (like some body functions) and harmful ones (like damage to cells or aging).
Key characteristics of free radicals
Key Characteristics:
Unstable and Reactive: Free radicals are unstable due to their unpaired electron and tend to cause chain reactions by stealing or sharing electrons with other molecules.
Formation: They are often formed during chemical reactions, like the breakdown of molecules under heat, light, or radiation.
Examples:
The chlorine radical (Cl·) in the reaction of chlorine with methane.
The hydroxyl radical (·OH), a common free radical in biological and environmental systems.
define electrophiles
Electrophiles are atoms, ions, or molecules that are attracted to electrons. They are electron-deficient and seek to gain electrons by reacting with electron-rich species (nucleophiles).
Electrophiles are essential in many chemical reactions, like substitution and addition reactions in organic chemistry.
Key Characteristics of Electrophiles
Key Characteristics:
Positive or Partially Positive: Electrophiles often have a positive charge (like H⁺) or a partial positive charge due to polar bonds.
Reactivity: They accept a pair of electrons during a chemical reaction, usually forming a covalent bond.
Examples:
H⁺ (proton): A common electrophile in acid-base reactions.
BF₃: An electrophile because boron is electron-deficient.
CH₃Cl (methyl chloride): The carbon is electrophilic because of the polar C-Cl bond.
Explain (and discus) reaction mechanisms
A reaction mechanism is a step-by-step explanation of how a chemical reaction happens at the molecular level. It describes the specific bonds that break, the new bonds that form, and the order in which these changes occur.
Explain where do reactions mechanisms come in handy
Understanding How Reactions Work
Mechanisms explain the step-by-step process of how reactants are converted into products.
They reveal what happens at the molecular level, such as bond-breaking and bond-forming.
2. Predicting Reaction Products
By analysing the mechanism, chemists can predict the main products and possible side products of a reaction, especially when multiple outcomes are possible.
3. Improving Reaction Efficiency
Mechanisms help identify inefficient steps or bottlenecks in a reaction, enabling chemists to optimise conditions (e.g., temperature, pressure, or catalyst choice).
4. Controlling Reaction Rates
Mechanisms show the rate-determining step, which is the slowest step in a reaction. By focusing on this step, chemists can speed up or slow down the reaction as needed.
5. Designing New Reactions
Understanding mechanisms allows chemists to develop new reactions or modify existing ones to produce desired compounds.
6. Explaining Selectivity
Mechanisms help explain why some reactions give specific products over others (e.g., in regioselective or stereoselective reactions).
7. Avoiding Dangerous Intermediates
Some reactions produce unstable intermediates (e.g., free radicals or carbocations). Knowing the mechanism helps predict and manage these intermediates safely.
Define a carbocation
A carbocation is an ion with a positively charged carbon atom. It is an intermediate formed during many chemical reactions, especially in organic chemistry.
Define homolytic fission
Homolytic fission is a type of bond breaking where a covalent bond splits evenly, and each atom involved in the bond takes one electron from the shared pair. This process produces two free radicals (species with unpaired electrons).
Key Points:
Equal Electron Sharing: Each atom gets one electron from the bond.
**Radical Formation: **The result is the formation of two highly reactive free radicals.
Occurs in Non-Polar Bonds: Homolytic fission typically happens in bonds where the two atoms have similar electronegativities.
Example:
When chlorine (Cl₂) undergoes homolytic fission:
Cl₂ → Cl· + Cl·
Each chlorine atom gets one electron, forming two chlorine radicals.
Homolytic fission often occurs under conditions like high temperature or the presence of UV light.
define heterolytic fission
Heterolytic fission is a type of bond breaking where a covalent bond splits unevenly, and one atom takes both electrons from the shared pair. This process results in the formation of two charged particles: a cation (positively charged) and an anion (negatively charged).
Key Points:
Unequal Electron Sharing: One atom gets both electrons from the bond, while the other gets none.
Ion Formation: A cation and an anion are produced.
Occurs in Polar Bonds: Heterolytic fission typically happens in bonds where one atom is more electronegative than the other.
Example:
When hydrogen chloride (HCl) undergoes heterolytic fission:
HCl → H⁺ + Cl⁻
The chlorine atom takes both electrons, forming a chloride ion (Cl⁻), while the hydrogen atom becomes a proton (H⁺).
Heterolytic fission is common in polar solvents or reactions involving highly electronegative atoms.
Define isomerism
Isomerism refers to the phenomenon where two or more compounds have the same molecular formula but different structures or arrangements of atoms. These compounds are called isomers.
define structural isomers
Have the same molecular formula but a different structural arrangement of atoms. They can be straight chains or branched chains but will have the same molecular formula.
