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)
Electrophile
+ve charged atoms, attracted to -ve charges (electron rich areas)
COMPLETE combustion of alkane
alkane ＋oxygen → CO2 ＋H2O
INCOMPLETE combustion of alkane
alkane ＋oxygen → CO ＋H2O
or
alkane ＋oxygen → C ＋H2O (soot)
how can you distinguish between alkane and alkene?
add the compound to bromine water (orange); if the compound is unsaturated, addition reaction will take place and the solution will decolorize
how to distinguish test for primary and secondary alcohol?
add **acidified potassium dichromate ** → strong color change from orange to green
use of alkane
fuels
use of alkene
make alcohol
(eg. ethanol, good solvent and fuel)
use of ester
perfume
addition polymerization
the reaction in which many monomers containing at least one C=C double bond form long chains of polymers
