Alkanes 09C Flashcards
general formula for cycloalkanes
CnH2n
physical properties: how the boiling point changes as the carbon chain increases
the boiling point increases regularly as the number of carbon atoms in chain increases
difference in bp between branched alkanes and straight-chain alkanes
the boiling point of branched chain alkanes are lower than straight chain alkanes, due to a smaller SA
how does the number of carbon atoms in an alkane affects the bp?
the more the number of carbon atoms, the more the number of electrons and hence the larger the electron cloud, leading to stronger dispersion forces, which require more energy to overcome.
why are the melting points of an alkane not as consistent as their boiling points?
the melting points are not only dependent on the size of the molecule, they are also dependent on the arrangement of molecules in a crystal lattice
substitution reactions: what are the requirements for Cl2 and Br2 to react?
presence of UV light or heat
what will be observed in the substitution reaction of Cl2 and Br2 respectively?
Cl2: greenish yellow Cl2 gas decolorised slowly.
Br2: reddish brown bromine liquid decolorized
What types of forces are present in alkanes? (between C and H atoms only)
Non polar, held together by weak dispersion forces as there is a very small dipole movement.
what will happen if an excess of halogens are added to a substitute reaction?
further substitutes of the product may occur, resulting in a multi substituted mix of halogenalkanes
what are the number of alkyl groups attached to primary, secondary and tertiary carbons?
1, 2, 3
for alkanes, what is the order of reactivity with halogens?
F2>Cl2>Br2>I2
- what are the bond angles in:
benzene
trigonal planar around all Cs, 120’, sp2 C
what reactions do alkanes undergo?
alkanes are generally unreactive, but it undergoes combustion and substitution.
