Structure and Bonding in Organic Chemistry

What is organic chemistry primarily concerned with?

The chemistry of carbon compounds.

What are the key concepts from general chemistry necessary for success in organic chemistry?

Electronic structure of the atom, Lewis structures, octet rule, types of bonding, electronegativity, and formal charges.

What types of bonding patterns should be predicted involving carbon and other elements?

Covalent and ionic bonding involving C, H, O, N, and the halogens.

What are resonance-stabilized structures?

Structures that can be represented by multiple Lewis structures, interconverted by moving electrons.

What types of structural formulas are commonly used in organic chemistry?

Condensed structural formulas and line-angle formulas.

How can the hybridization and geometry of organic molecules be predicted?

Based on their bonding.

What are isomers?

Compounds that have the same molecular formula but different structures.

What is an ionic bond?

A bond formed by the transfer of electrons from one atom to another, resulting in opposite charges that attract each other.

What characterizes a covalent bond?

Electrons are shared between atoms to complete the octet.

What is a nonpolar covalent bond?

A bond where electrons are shared equally between atoms, such as C-C or C-H bonds.

What is a polar covalent bond?

A bond where electrons are shared unequally, such as C-O or C-N bonds.

What is the purpose of formal charges in molecules?

To keep track of electrons, which may or may not correspond to actual charges.

What are resonance forms?

Lewis structures that can be interconverted by moving electrons only.

What criteria are used to compare resonance forms?

1. Has as many octets as possible; 2. Has as many bonds as possible; 3. Has the negative charge on the most electronegative atom; 4. Has as little charge separation as possible.

What defines the major contributor among resonance forms?

The one in which all the atoms have a complete octet of electrons.

When both resonance forms obey the octet rule, how is the major contributor determined?

The major contributor is the one with the negative charge on the most electronegative atom.

What is the significance of charge separation in resonance forms?

The most stable resonance form has the smallest separation of oppositely charged atoms.

What should be done when moving electrons in resonance structures?

Do NOT move atoms.

What is the role of electronegativity in determining resonance structure stability?

The negative charge should be placed on the most electronegative atom for greater stability.

What is the octet rule?

Atoms tend to form bonds until they are surrounded by eight valence electrons.

What is the relationship between resonance forms and the true structure of a molecule?

The true structure is a hybrid of the contributing resonance forms.

What happens to acetic acid when it loses a proton?

It forms the acetate ion, which has a negative charge delocalized over both oxygen atoms.

How does the delocalization of charge in the acetate ion affect its stability?

It stabilizes the ion by allowing each oxygen atom to bear half of the negative charge.

What is the bond order of the carbon-oxygen bonds in the acetate ion?

1½, indicating that each bond is halfway between a single bond and a double bond.

What are the three types of structural formulas mentioned?

1. Lewis Structure 2. Condensed Structural Formula 3. Line and Angle Formula

What is a condensed structural formula?

It is written without showing all individual bonds, listing atoms bonded to the central atom after it.

How are identical groups represented in condensed structural formulas?

Using parentheses and a subscript.

What is a line-angle drawing?

A skeletal structure where bonds are represented by lines and carbons are implied at the ends and intersections of lines.

What must be shown in line-angle drawings?

Nitrogen, oxygen, halides, and double or triple bonds must be explicitly shown.

What does the molecular formula represent?

It gives the number of atoms of each element in one molecule of a compound.

What is the empirical formula of butan-1-ol (C4H10O)?

The empirical formula is the same as the molecular formula, C4H10O.

What is the difference between bond formation and hybridization?

Bond formation involves combining orbitals between different atoms, while hybridization involves combining orbitals on the same atom.

What is the hybridization and geometry of sp hybrid orbitals?

Hybridization is sp, and the geometry is linear with approximate bond angles of 180°.

What is the hybridization and geometry of sp2 hybrid orbitals?

Hybridization is sp2, and the geometry is trigonal with approximate bond angles of 120°.

What is the hybridization and geometry of sp3 hybrid orbitals?

Hybridization is sp3, and the geometry is tetrahedral with approximate bond angles of 109.5°.

What characterizes sigma bonding?

It involves head-to-head overlap of orbitals, with electron density lying between the nuclei.

What types of orbital overlaps can form sigma bonds?

s—s, p—p, s—p, or hybridized orbital overlaps.

What is pi bonding?

It is characterized by the sideways overlap of two parallel p orbitals, leading to a π-bonding molecular orbital.

How does the strength of a pi bond compare to a sigma bond?

A pi bond is not as strong as most sigma bonds.

What constitutes a double bond?

A double bond consists of one sigma bond and one pi bond.

What constitutes a triple bond?

A triple bond consists of one sigma bond and two pi bonds.

How many sigma bonds are formed in ethylene, and what is its hybridization?

Ethylene has three sigma bonds formed by sp2 hybrid orbitals in a trigonal planar geometry.

What is the relationship between the unhybridized p orbital of one carbon and the sp2 hybrid orbitals of another carbon in acetylene?

The unhybridized p orbital of one carbon is perpendicular to its sp2 hybrid orbitals and parallel to the unhybridized p orbital of the second carbon.

What type of bond is formed by the overlap of two p orbitals in acetylene?

A pi bond (double bond) that is located above and below the sigma bond.

What is the main characteristic of single bonds in terms of molecular rotation?

Single bonds are allowed to rotate, giving a variety of conformations.

Can double bonds rotate?

No, double bonds cannot rotate.

What happens to compounds that differ in the arrangement of their substituents around a double bond?

They can be isolated and separated.

What theory is used to explain molecular shapes and bond angles?

Valence-shell electron-pair repulsion theory (VSEPR).

Why are hybridized orbitals lower in energy compared to standard orbitals?

Because electron pairs are farther apart.

How do you determine the number of hybrid orbitals on an atom?

By adding the number of sigma bonds and the number of lone pairs of electrons on that atom.

What is the hybridization and bond angle for sp hybrid orbitals?

Hybridization is sp with a linear geometry and a bond angle of 180°.

What is the hybridization and bond angle for sp2 hybrid orbitals?

Hybridization is sp2 with a trigonal planar geometry and a bond angle of 120°.

What is the hybridization and bond angle for sp3 hybrid orbitals?

Hybridization is sp3 with a tetrahedral geometry and a bond angle of 109.5°.

What are constitutional isomers?

Isomers that differ in their bonding sequence.

What distinguishes stereoisomers from constitutional isomers?

Stereoisomers differ only in the arrangement of the atoms in space.

What are the properties of constitutional isomers?

They have the same chemical formula but are connected in a different order and have different properties.

How does the number of isomers change with the number of carbon atoms?

The number of isomers increases rapidly as the number of carbon atoms increases.

What are cis and trans isomers?

They are types of stereoisomers that occur when there is a double bond in the compound.

What is a key feature of geometric stereoisomers?

They have the atoms bonded in the same order but different orientations in space.

Why do cis and trans isomers occur in compounds with double bonds?

Because there is no free rotation along the carbon-carbon double bond.

What is the significance of the arrangement of groups on carbons in geometric isomers?

The groups can point to different places in space due to the restricted rotation around the double bond.