Amines
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What are amines? (deriv. - NH3 - H atoms rep. - R groups)
Derivatives of ammonia (NH₃) in which one or more hydrogen atoms are replaced by alkyl or aryl groups
Draw the displayed formula of ammonia
H | H–N–H ..
General displayed formula of a primary (1°) amine
H | R–N–H ..
General displayed formula of a secondary (2°) amine
R | R–N–H ..
General displayed formula of a tertiary (3°) amine
R | R–N–R
What do 1°, 2°, and 3° mean in amines?
They refer to the number of R groups attached to the nitrogen atom
How does the meaning of: 1°, 2°, and 3° differ in alcohols compared to amines? (Ami. = R - N, Alc. = R - C-OH)
Amines use it to number the R groups attached to the nitrogen whereas alcohols use it to number the R groups attached to the carbon bonded to the -OH
General formula of a primary amine?
RNH₂
How are amines named?
Using either the suffix, -amine or the prefix, -amino
Name and draw the amine CH₃NH₂
methylamine
Name and draw the amine: C₆H₅NH₂
Phenyl amine
What is the shape and bond angle of an ammonia molecule, and therefore an amine molecule?
Trigonal pyramidal, 107°
Why is the bond angle in ammonia less than 109.5°?
The lone pair on nitrogen repels more strongly than bonding pairs, compressing the bond angle
Are amines polar molecules?
Yes
Why can primary amines hydrogen bond to each other? (cont. N-H bnd. - H bonds)
They contain N-H bonds allowing hydrogen bonding between molecules
How does hydrogen bonding in amines compare to alcohols? (weakness, electronegativity)
Hydrogen bonding in amines is weaker than in alcohols because nitrogen is less electronegative than oxygen
How do boiling points of amines compare to alcohols? (ami. low < alc. - wkr h. bonds < alc. - N< elec.neg. alc.)
Amines have lower boiling points than compare to alcohols because they form weaker hydrogen bonds than alcohols, since nitrogen is less electronegative than oxygen
What is the physical state of short - chain amines at room temperature? (short = g, long = l)
Short chain amines are gases at room temperature and slightly longer chains are volatile liquids
What smell do amines have, and why?
Fishy smells, due to di- and triamines produced during protein decomposition
Why are short chain primary amines soluble in water?
They form hydrogen bonds with water
Why is phenylamine poorly soluble in water? (b ring - no H bonds - red. sol.)
The benzene ring cannot form hydrogen bonds reducing solubility
Why are amines reactive?
They have a lone pair of electrons on the nitrogen atom
What two types of reactions does the lone pair in amines take part in? (B+N)
Base reactions and nucleophilic reactions
How do amines act as bases, and what type of bases are amines? (wk. bses. - lp. - N - H+ - B.L. bases)
Amines act as weak bases, the lone pair on the nitrogen accepts a H+ ion, allowing them to act as brønsted–lowry bases