Carbon is Simply Amazing. Ch 4

2. Carbon atoms are the most versatile building blocks of molecules With a total of 6 electrons, a carbon atom has 2 in the first shell and 4 in the second shell. Carbon has little tendency to form ionic bonds by loosing or gaining 4 electrons. Instead, carbon usually completes its valence shell by sharing electrons with other atoms in four covalent bonds. This tetravalence by carbon makes large, complex molecules possible. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 4.4 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

FUNCTIONAL GROUPS! Why do we care about functional groups anyway? (Besides the fact that they’re on the AP Test?) See next slide for an example of its importance!

1. Functional groups contribute to the molecular diversity of life The components of organic molecules that are most commonly involved in chemical reactions are known as functional groups. Functional groups are attachments that replace one or more hydrogen atoms to the carbon skeleton of the hydrocarbon. Each functional groups behaves consistently from one organic molecule to another. The number and arrangement of functional groups help give each molecule its unique properties. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

There are six functional groups that are most important to the chemistry of life: hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, and phosphate groups. All are hydrophilic and increase solubility of organic compounds in water. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

In a hydroxyl group (-OH), a hydrogen atom forms a polar covalent bond with an oxygen which forms a polar covalent bond to the carbon skeleton. Because of these polar covalent bonds hydroxyl groups improve the solubility of organic molecules. Organic compounds with hydroxyl groups are alcohols and their names typically end in -ol. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A carbonyl group (=CO) consists of an oxygen atom joined to the carbon skeleton by a double bond. If the carbonyl group is on the end of the skeleton, the compound is an aldelhyde. If not, then the compound is a ketone. Isomers with aldehydes versus ketones have different properties. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A carboxyl group (-COOH) consists of a carbon atom with a double bond with an oxygen atom and a single bond to a hydroxyl group. Compounds with carboxyl groups are carboxylic acids. A carboxyl group acts as an acid because the combined electronegativities of the two adjacent oxygen atoms increase the dissociation of hydrogen as an ion (H+). Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

An amino group (-NH2) consists of a nitrogen atom attached to two hydrogen atoms and the carbon skeleton. Organic compounds with amino groups are amines. The amino group acts as a base because ammonia can pick up a hydrogen ion (H+) from the solution. Amino acids, the building blocks of proteins, have amino and carboxyl groups. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A sulfhydryl group (-SH) consists of a sulfur atom bonded to a hydrogen atom and to the backbone. This group resembles a hydroxyl group in shape. Organic molecules with sulfhydryl groups are thiols. Sulfhydryl groups help stabilize the structure of proteins. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A phosphate group (-OPO32-) consists of phosphorus bound to four oxygen atoms (three with single bonds and one with a double bond). A phosphate group connects to the carbon backbone via one of its oxygen atoms. Phosphate groups are anions with two negative charges as two protons have dissociated from the oxygen atoms. One function of phosphate groups is to transfer energy between organic molecules. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

2. The chemical elements of life: a review Living matter consists mainly of carbon, oxygen, hydrogen, and nitrogen, with smaller amounts of sulfur and phosphorus. These elements are linked by strong covalent bonds. Carbon with its four covalent bonds is the basic building block in molecular architecture. The great diversity of organic molecules with their special properties emerge from the unique arrangement of the carbon skeleton and the functional groups attached to the skeleton. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Testing…HYDROXYL What is the functional group? It is POLAR (that bond between oxygen and hydrogen look familiar?) and it makes a molecule that is attached to it WATER SOLUBLE. Anything with a hydroxyl is called an alcohol.

Testing…Carbonyl? What is the functional group? It is POLAR. So anything with this functional group is WATER SOLUBLE. It is found in sugars. Aldehyde…ketone?

Testing…CARBOXYL Also polar. But that covalent bond between oxygen and hydrogen is so very polar that the hydrogen reversibly dissociates as H+ Since it donates protons, this group might have what kind of properties? Compounds with this group are called carboxylic acids.

Testing…AMINO Again, it’s POLAR and soluble in water/ Because it’s unshared pair of electrons on the nitrogen can accept a proton (a H+), amino acts a a weak base. Any compound with an amino functional group is called an amine.

Testing…Sulfhydryl This has an atom of sulfur + an atom of hydrogen (-SH) Helps stabilize the structure of proteins Organic compounds with this functional group are called thiols

Testing…Phosphate This functional group has a disassociated form of phosphoric acid Phosphate has acidic properties.

Add On…Methyl Methyl (-CH3) can be considered a functional group. Unlike all the others we talked about, it is NONPOLAR and therefore HYDROPHOBIC These properties will make it useful when we talk about tertiary structure in proteins

For the Quiz… You should have the structures memorized in picture form (That includes the difference between single and double bonds, and where these are placed.) You should know where these functional groups are found. You should know what they are called.

Variations in Carbon Skeletons Hydrocarbons=molecules that include only carbon and hydrogen -these are major components of fossil fuels -framework for the diverse molecules found in living organisms -these are hydrophobic (WHY?) Think: C-H bonds and C-C bonds…

The Three Types of Isomers Definition of Isomer= compound with the same molecular formula but with different structures and hence, different properties

Structural Isomer Isomers that differ in the covalent arrangement of atoms May also differ in location of double bonds

Geometric Isomer Isomers share the same covalent partnerships, but differ in spatial arrangements Due to fact that double bonds DO NOT allow atoms they join to ROTATE FREELY

Enantiomer Mirror images of each other Two different spatial arrangements around asymmetric carbon Usually one is biologically active and other is not

Even the subtle structural differences in two enantiomers have important functional significance because of emergent properties from the specific arrangements of atoms. One enantiomer of the drug thalidomide reduced morning sickness, its desired effect, but the other isomer caused severe birth defects. The L-Dopa isomer is an effective treatment of Parkinson’s disease, but the D-Dopa isomer is inactive. Fig. 4.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings