Reaction Mechanisms Flashcards
(26 cards)
What two ways can a covalent bond be cleaved? (eg: Homolytic and Heterolytic)
- Symmetrically (homolytic): Each atom gets one electron, forming radicals (neutral species with an unpaired electron) eg: A-B –> *A + *B
- Unsymmetrically (heterolytic) : Electrons move to one atom, creating ions (cation and anion) eg: A-B –> A- + B+ this uses fishhook arrows
What does carbocation formation indicate in a reaction?
Indicates electron movement towards a carbon, typically with a highly electronegative halogen (like chlorine). Would react differently than a carbanion, which would typically react with a metal.
What are the three relative stabilities of carbocations and their geometric shape?
- Tertiary carbocations are most stable
- Secondary carbocations are intermediate
- Primary carbocations are least stable
Geometrically: sp2 hybridized and flat
What does ‘reaction mechanism’ mean?
A detailed description of how a chemical reaction occurs, capturing the full pathway of electron movements, bond breaking, and bond forming steps.
What is a substitution reaction? (dont forget to mention sigma/pi bonds here)
A reaction where one group is replaced by another, typically involving breaking and forming single sigma bonds.
What is an addition reaction?
A reaction where multiple (pi) bonds are broken and replaced with single (sigma) bonds, typically adding groups across a double or triple bond.
What is an elimination reaction?
A reaction where two single bonds are formed on adjacent atoms, typically removing groups to create a multiple (pi) bond(s).
What does nucleophile mean?
A species that seeks positive charges, donates electrons, and forms new bonds. Literally means ‘nucleus-loving’.
What does electrophile mean?
A species that seeks negative charges, accepts electrons. Literally means ‘electron-loving’.
What is a polar bond?
A chemical bond where electrons are unequally shared due to difference in electronegativity between atoms, creating partial charges.
What is a non-polar bond?
A chemical bond where electrons are equally shared between atoms of similar electronegativity, with no significant charge separation.
What are some high polarity groups?
Carboxyl (-COOH), Hydroxyl (-OH), Amine (-NH2, -NR2), and Phosphate (-PO4^-3)
What are some moderately polar groups?
Ketone (C=O), Aldehyde (-CHO), Ester (-COO-), Amide (-CONH2) // These have dipole interactions but may not form hydrogen bonds as strongly as highly polar groups
What are some non-polar functional groups?
Alkanes (-CH3, -CH2), Aromatic rings (eg: benzene), Ether (-O-)
What does TLC stand for?
Thin layer Chromatography
What does Rf stand for (in chromatography) ?
Retention factor
What is chromatography, its purpose and its relationship to solubility?
Used to seperate and analyse compounds’ polarity and solubility in a solvent. If a compound is more polar, it is more soluble and therefore move less and have a lower Rf because it interacts with the stationary phase of the TLC more. If a compound is more non-polar and less soluble it moves faster in the TLC and therefore has a higher Rf
What are momentary dipole to dipole forces?
Temporary shifts in electron density that have momentary dipoles between electron clouds, weak interactions; all molecules experience it, but non-polar molecules only experience this type of interaction (eg: O2) Strength increases with increasing in molecule size
What are the 3 types of Intermolecular forces?
1- Momentary dipole to dipole forces 2- Dipole to dipole forces 3- Hydrogen bonding
What are dipole to dipole interactions?
Attraction between permanent dipoles in polar molecules (eg: HCl) stronger than Momentary dipole to dipole interactions, but weaker than Hydrogen bonding
What is hydrogen bonding?
Strongest IMF, occurring when H is bonded to N, O, or F and interacts with a lone pair on another N, O, or F. (eg: H2O, -OH groups)
What’s the difference between instantaneous rate and Average rate in reactions?
Instantaneous is how fast/slow reaction is occurring at any instant
Average rate is how fast/slow over extended period of time
What is a third-order reaction? What units and rate law?
In a third-order reaction, the rate depends on the concentration of one reactant raised to the third power or the product of concentrations of multiple reactants.
-Units: L^2 mol^-2 s^-1
-Rate Law: k[A]^3 OR k[A]^2[B] OR k[A][B][C]
What is a second-order reaction? What units and rate law?
In a second-order reaction, the rate is proportional to the square of the concentration of one reactant or the product of the concentrations of two reactants.
-Units: L mol^-1 s^-1
-Rate Law: k[A][B] OR k[A]^2
