10 Organic Chemistry Flashcards
free radical
has unpaired electrons → very reactive, used for substitution with alkanes
homolytic fission (homolysis)
when a covalent bond breaks by splitting the shared pair of bonding electrons; produces two free radicals (each has an unpaired electron)
heterolytic fission (heterolysis)
when a covalent bond breaks by splitting the shared pair of bonding electrons, but both electrons go to one of the product; produces two oppositely charged ions
Explain how we obtain free radicals
- diatomic molecule (Cl2) undergoes homolysis - when exposed to UV light → a bond breaks → each atom gains one of the bonding electrons
Explain the process of free radical substitution
- INITIATION: Cl-Cl bond is broken by energy from the UV light, forming two free radicals
- PROPAGATION: the free radicals are very reactive and will attack the unreactive alkanes → C-H bond breaks homolytically and each atom gets an electron → another free radical is produced → attack another Cl molecule to form halogenoalkane → regenerate the Cl free radical → repeats…
- TERMINATION: the chain reaction stops when two free radicals react to form a single unreactive molecule
homologous series
same functional group/general formula = same chemical properties
different number of carbon atoms (each member differ by CH2）= gradually changing physical properties
Explain the trend of boiling point across homologous series
each homologous increment (additional CH2) adds 8 more electrons → increased strength of LDF → more energy needed to break the bond, higher BP
Explain why aldehyde and ketone have higher boiling points and are soluble in water
The difference in electronegativity between C and O means the C=O bond is polar → stronger dipole dipole attraction, more obvious for small molecules as the polar bond takes a large overall proportion!
Explain why carboxylic acids are soluble in water and have higher boiling points than their functional group isomers esters
hydrogen bond between O and H in carboxylic acids is polar and stronger
isomer
compounds that have same molecular formulae but different arrangement of atoms
there are positional, chain, and functional group isomers - should know how to identify them
Primary, secondary, and tertiary alcohol/halogenoalkanes
C atoms bonded to the functional group is attached to 1/2/3 other C atom (or functional group)
Explain why benzene is very stable
The benzene ring has delocalized π electrons → electron density is spread out over the molecule instead of being confined to a small area
Why are halogenoalkanes much more reactive than alkanes?
halogens are electronegative, so the halogen-carbon bond is polar, carbon partial +ve and halogen partial -ve → partial
-ve halogen attracts nucleophiles and undergo nucleophilic substitution
Why are alkanes unreactive?
Saturated (strong) single bonds; C and H have similar electronegativity → non-polar, no electron-rich or -deficient areas → doesn’t attract electrophiles or nucleophiles
Nucleophile
-ve charged atoms, attracted to +ve charges (electron deficient areas)
