Pages 13-20 provide you with examples of molecules that have the functional group identified on that page. Use these examples to help you spot the key features (atom connections) of each functional group Properties of molecules: • page 21: Organic Acids & bases • page 22-23: Functional groups in biology: amino acids, proteins, DNA CHEM 110 4
ALKYNES are hydrocarbons that contain one or more triple bonds ethyne propyne (acetylene) 1-butyne 2-butyne Mary J. Bojan 5 General formula for alkynes with only one triple bond: C n H 2n-2 Constitutional isomers are possible. No geometric isomers are possible. C C H C H H C H H H C C C C H H H H H H Chem 110 Aromatic Hydrocarbons Contain alternating C-C single and double bonds Benzene is the prototypical molecule Mary J. Bojan 6 Usually written: Aromatic hydrocarbons are less reactive than alkenes: We can draw resonance structures: resonance implies added stability C C C C C C H H H H H H C C C C C C H H H H H H Chem 110
These are other examples of aromatic hydrocarbons. Mary J. Bojan 7 - All of these have resonance structures. - All have the added stability associated with resonance. - Recall that resonance means that delocalized π bonding exists in the molecule. Chem 110 DEMO: Reactivity of Hydrocarbons Same reaction: hydrocarbon (colorless) + Br 2 (red) Mary J. Bojan Chem 110 8 No reaction No reaction Reaction occurs instantly
Recall from Chapter 9: Delocalized π bonding explains the stability of aromatic hydrocarbons. Alkene + Br 2 reacts readily Aromatic + Br 2 no reaction • π bonds of alkenes and alkynes are very reactive • π -bonds in aromatics are NOT reactive due to the extra stability of delocalized π system Mary J. Bojan 9 Chem 110 Polarity in organic molecules Compare substituted benzene rings: if bond dipoles cancel, the molecule will not be polar. Geometric isomers: Compare cis- and trans- dichloroethylene cis is polar trans is nonpolar bond dipoles add bond dipoles cancel Chem 110 Mary J. Bojan 10 C C Cl H H Cl C C H H Cl Cl cis dichloroethylene trans dichloroethylene Cl Cl polar Cl Cl polar Cl Cl Cl Cl Cl nonpolar nonpolar
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- Fall '17
- Joseph Houck
- Amine, Carboxylic acid, Functional group, Amide, Mary J. Bojan