4. Carbon Flashcards
Organic Compounds contain ____?
What Atoms are commonly present in organic compounds?
What makes large complex molecules possible?
What are some examples of Organic Compounds?
How many electrons does carbon have?
How many electrons in the first and second shell?
How many Valence Electrons?
How many covalent bonds can carbon make?
Carbon has 6 electrons, with 2 in the first electron shell and 4 in the second shell; thus, it has 4 valence electrons in a shell that can hold up to 8 electrons.
A carbon atom usually completes its valence shell by sharing its 4 electrons with other atoms so that 8 electrons are present. Each pair of shared electrons constitutes a covalent bond (see Figure 2.10d).
In organic molecules, carbon usually forms single or double covalent bonds. Each carbon atom acts as an intersection point from which a molecule can branch off in as many as four directions. This enables carbon to form large, complex molecules.
The Formation of Bonds with Carbon
When a carbon atom forms four single covalent bonds, the arrangement of its four hybrid orbitals causes the bonds to angle toward the corners of an imaginary tetrahedron. The bond angles in methane (CH4) are 109.5° (Figure 4.3a), and they are roughly the same in any group of atoms where carbon has four single bonds. For example, ethane (C2H6) is shaped like two overlapping tetrahedrons (Figure 4.3b). In molecules with more carbons, every grouping of a carbon bonded to four other atoms has a tetrahedral shape. But when two carbon atoms are joined by a double bond, as in ethene (C2H4), the bonds from both carbons are all in the same plane, so the atoms joined to those carbons are in the same plane as well (Figure 4.3c). We find it convenient to write molecules as structural formulas, as if the molecules being represented are two-dimensional, but keep in mind that molecules are three-dimensional and that the shape of a molecule is central to its function.
Molecular Diversity Arising from Variation in Carbon Skeletons:
- Carbon chains form the skeletons of most organic molecules.
- The skeletons vary in length and may be straight, branched, or arranged in closed rings.
- Some carbon skeletons have double bonds, which vary in number and location.
- Such variation in carbon skeletons is one important source of the molecular complexity and diversity that characterize living matter.
- In addition, atoms of other elements can be bonded to the skeletons at available sites.
Hydrocarbons
- Hydrocarbons, organic molecules consisting of only carbon and hydrogen.
- Atoms of hydrogen are attached to the carbon skeleton wherever electrons are available for covalent bonding.
- Although hydrocarbons are not prevalent in most living organisms, many of a cell’s organic molecules have regions consisting of only carbon and hydrogen. For example, the molecules known as fats have long hydrocarbon tails attached to a nonhydrocarbon component.
- Neither petroleum nor fat dissolves in water; both are hydrophobic compounds because the great majority of their bonds are relatively nonpolar carbon-to-hydrogen linkages.
- Another characteristic of hydrocarbons is that they can undergo reactions that release a relatively large amount of energy.
- The gasoline that fuels a car consists of hydrocarbons, and the hydrocarbon tails of fats serve as stored fuel for plant embryos (seeds) and animals.
What is an Isomer
Compounds with the same molecular formula but different chemical structures and hence different properties
What is a constitutional isomer?
Their atoms are connected in a different order.
What are Stereoisomers?
Their atoms are connected in a same order
But these isomers have a different geometry.
Types of Isomers covered:
Structural Isomers
- Structural isomers differ in the covalent arrangements of their atoms.
- Structural isomers may also differ in the location of double bonds.
- The number of possible isomers increases tremendously as carbon skeletons increase in size.
Cis-trans isomers
In cis-trans isomers, carbons have covalent bonds to the same atoms, but these atoms differ in their spatial arrangements due to the inflexibility of double bonds.
Single bonds allow the atoms they join to rotate freely about the bond axis without changing the compound. In contrast, double bonds do not permit such rotation. If a double bond joins two carbon atoms, and each C also has two different atoms (or groups of atoms) attached to it, then two distinct cis-trans isomers are possible.
Consider a simple molecule with two double-bonded carbons, each of which has an H and an X attached to it (Figure 4.7b). The arrangement with both Xs on the same side of the double bond is called a cis isomer, and that with the Xs on opposite sides is called a trans isomer. The subtle difference in shape between such isomers can have a dramatic effect on the biological activities of organic molecules. For example, the biochemistry of vision involves a light-induced change of retinal, a chemical compound in the eye, from the cis isomer to the trans isomer (see Figure 50.17).
Enantiomers
Enantiomers are isomers that are mirror images of each other and that differ in shape due to the presence of an asymmetric carbon, one that is attached to four different atoms or groups of atoms.
The four groups can be arranged in space around the asymmetric carbon in two different ways that are mirror images.
Analogy: Enantiomers are, in a way, left-handed and right-handed versions of the molecule. Just as your right hand won’t fit into a left-handed glove, a “right-handed” molecule won’t fit into the same space as the “left-handed” version. Usually, only one isomer is biologically active because only that form can bind to specific molecules in an organism.
The concept of enantiomers is important in the phar- maceutical industry because the two enantiomers of a drug may not be equally effective, as is the case for both ibu- profen and the asthma medication albuterol (Figure 4.8). Methamphetamine also occurs in two enantiomers that have very different effects. One enantiomer is the highly addictive stimulant drug known as “crank,” sold illegally in the street drug trade. The other has a much weaker effect and is the active ingredient in an over-the-counter vapor inhaler for treatment of nasal congestion. The differing effects of enantiomers in the body demonstrate that organisms are sensitive to even the subtlest variations in molecular architecture. Once again, we see that molecules have emergent properties that depend on the specific arrangement of their atoms.
Functional groups
The components of organic molecules
that are most commonly involved in chemical reactions
Functional groups are the components of organic molecules that are most commonly involved in chemical reactions
The number and arrangement of functional groups give each molecule its unique properties
