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Chapter 2
Structure and Properties of Organic Molecules

02-05

Title	Representation of a Bonding Molecular Orbital.
Caption	Figure 2-5A bonding molecular orbital places a large amount of electron density in the bonding region, the space between the two nuclei.
Notes	The distance at which the two nuclei neither attract nor repel each other is called bond length, and at this distance both forces are balanced. The region between the nuclei is called the bonding region and it is the region in which the electrons are most likely to be found.
Keywords	nucleus, electron, orbital, electron density, bonding region, bond length

02-06

Title	Formation of a s-bonding Molecular Orbital
Caption	Figure 2-6Formation of a s-bonding MO. When the 1s orbitals of two hydrogen atoms overlap in phase with each other, they interact constructively to form a bonding MO. The electron density in the bonding region (between the nuclei) is increased. The result is a cylindrically symmetrical bond, or sigma bond.
Notes	A bonding molecular orbital is the result of the constructive interaction between two 1s orbitals of hydrogen when they overlap. The bonding MO formed is called a sigma bond and it is the most common bond in organic compounds.
Keywords	bonding molecular orbital, constructive overlap, sigma bond

02-07

Title	Formation of a s-antibonding Molecular Orbital
Caption	Figure 2-7Formation of a s* antibonding MO. When two 1s orbitals overlap out of phase, they interact destructively to form an antibonding MO. The positive and negative values of the wave functions tend to cancel out in the region between the nuclei, and a node separates the nuclei. We use an asterisk () to designate antibonding orbitals; this sigma antibonding orbital is symbolized by s.
Notes	When the interaction between two 1s orbitals of hydrogen is destructive, an antibonding molecular orbital is formed. An antibonding MO is a node or a nodal plane separating the two atoms.
Keywords	destructive interaction, antibonding molecular orbital, node, nodal plane

02-08

Title	Molecular Orbitals of Hydrogen
Caption	Figure 2-8When the two hydrogen 1s orbitals overlap, a sigma bonding MO and a sigma antibonding MO result. Two electrons (represented by arrows) go into the bonding MO with opposite spins, forming a stable H2 molecule.
Notes	When two 1s orbitals overlap, two molecular orbitals are formed; a bonding MO (s) and an antibonding MO (s*). Bonding MO are lower in energy than the antibonding MO. The two electron of the H2 molecule occupy the bonding MO with opposite spins.
Keywords	orbital overlap, molecular orbitals, bonding MO, antibonding MO

02-08-01UN

Title	Formation of a s-bonding MO from p Orbitals
Caption	When two p orbitals overlap along the line between the nuclei, a bonding orbital and an antibonding orbital result. Once again, most of the electron density is centered along the line between the nuclei. This linear overlap is another type of sigma bonding MO. The constructive overlap of two p orbitals along the line joining the nuclei forms a s bond represented as follows:
Notes	Two p orbitals will overlap with each other to form two molecular orbitals; a bonding MO (shown) and an antibonding MO (not shown). The sigma bonding MO has its electron region between the two nuclei.
Keywords	p orbital, molecular orbital

02-09

Title	Formation of Pi Molecular Orbitals
Caption	Figure 2-9The sideways overlap of two p orbitals leads to a pi bonding MO and a pi antibonding MO. A pi bond is not as strong as most sigma bonds.
Notes	Two parallel p orbitals can overlap constructively to form a pi-bonding MO. The two p orbitals will also overlap destructively with each other forming a pi*-antibonding MO. The pi bond (p-bond, a double bond) can only form once there is a sigma bond formed between the atoms.
Keywords	p orbitals, constructive overlap, destructive overlap, bonding MO, antibonding MO

02-10

Title	Molecular Orbitals of a Double Bond
Caption	Figure 2-10The second bond of a double bond is a pi bond. The pi bond has its electron density centered in two lobes, above and below the sigma bond. Together, the two lobes of the pi bonding molecular orbital constitute one bond.
Notes	Once a sigma bond is formed between the atoms, the two parallel p orbitals will overlap with each other to form the bonding and antibonding molecular orbitals. The lobes of the pi bond are located above and below the sigma bond.
Keywords	sigma bond, pi bond, single bond, double bond, molecular orbital

02-11

Title	Structures of Methane, Ethylene, and Acetylene
Caption	Figure 2-11The angles between the p orbitals are all 90¡, but few organic compounds have bond angles of 90¡. Their bond angles are usually close to 109¡, 120¡, or 180¡.
Notes	The bond angle of sp3 hybrid orbitals is 109.5¡; the bond angle for sp2 hybrid orbitals is around 120¡; the bond angle for sp hybrid orbitals is 180¡.
Keywords	bond angle, hybrid orbital

02-12

Title	sp Hybrid Orbitals
Caption	Figure 2-12Addition of an s orbital to a p orbital gives an sp hybrid atomic orbital, with most of its electron density on one side of the nucleus. Adding the p orbital with opposite phase gives the other sp hybrid atomic orbital, with most of its electron density on the opposite side of the nucleus from the first hybrid.
Notes	Hybrid orbitals are the result of adding orbitals of the same atom. Addition of an s orbital to a p orbital results in the formation of two sp hybrid orbitals. These two sp orbitals are at an angle of 180¡ degrees from each other.
Keywords	hybrid orbital

02-14

Title	sp2 Hybrid Orbitals
Caption	Figure 2-14Hybridization of an s orbital with two p orbitals gives a set of three sp2 hybrid orbitals. The bond angles associated with this trigonal structure are about 120¡. The remaining p orbital is perpendicular to the plane of the three hybrid orbitals.
Notes	Adding one s orbital to two p orbitals forms three sp2 orbitals. These hybrid orbitals are at a 120¡ angle from each other in a trigonal planar geometry.
Keywords	hybrid orbitals, trigonal planar

02-15

Title	sp3 Hybrid Orbitals
Caption	Figure 2-15Hybridization of an s orbital with all three p orbitals gives four sp3 hybrid orbitals with tetrahedral geometry and 109.5¡ bond angles.
Notes	Each sp3 hybrid orbital is pointing toward the corners of a tetrahedron at an angle of 109.5¡ from each other.
Keywords	hybrid orbital, tetrahedral geometry, bond angle

02-16

Title	Methane Representations
Caption	Figure 2-16Methane has tetrahedral geometry, using four sp3 hybrid orbitals to form sigma bonds to the four hydrogen atoms.
Notes	A carbon with four single bonds will have a tetrahedral geometry. The simplest carbon compound is methane (CH4).
Keywords	hybrid orbitals, sigma bonds, tetrahedral geometry

02-16-02UN

Title	Drawing 3-dimensional Structures
Caption	The three-dimensional structure of ethane, C2H6, has the shape of two tetrahedra joined together. Each carbon atom is sp3 hybridized, with four sigma bonds formed by the four sp3 hybrid orbitals. Dashed lines represent bonds that go away from the viewer, wedges represent bonds that come out toward the viewer, and other bond lines are in the plane of the paper. All the bond angles are close to 109.5¡
Notes	It is easier to grasp this concept by working with molecular models and building the different molecules. Bonds that are on the plane of the paper are drawn with single lines; bonds that point away from the plane of the paper are drawn with dashed lines; bonds that are in front of the plane of the paper are drawn with wedges.
Keywords	3-dimensional structures, dash, wedge, plane, bond

02-17

Title	Bonding in Ethylene
Caption	Figure 2-17The carbon atoms in ethylene are sp2 hybridized, with trigonal bond angles of about 120¡. All the carbon and hydrogen atoms lie in the same plane.
Notes	Ethylene has three (3) sigma bonds formed by its sp2 hybrid orbitals in a trigonal planar geometry. The unhybridized p orbital of one carbon is perpendicular to its sp2 hybrid orbitals and it is parallel to the unhybridized p orbital of the second carbon. Overlap of these two p orbitals will produce a pi bond (double bond) which is located above and below the sigma bond.
Keywords	hybrid orbital, unhybridized, sigma bond, pi bond, double bond

02-18

Title	Bonding in Acetylene
Caption	Figure 2-18The carbon atoms in acetylene are sp hybridized, with linear (180¡) bond angles. The triple bond contains one sigma bond and two perpendicular pi bonds.
Notes	Acetylene has two (2) sigma bonds formed by its sp hybrid orbital in a linear geometry. The two unhybridized p orbitals of one carbon are perpendicular to its sp hybrid orbital and are parallel to the unhybridized p orbitals of the second carbon. Overlap of these four p orbitals will produce two pi bonds (triple bond) which are located above and below the sigma bond.
Keywords	hybrid orbital, unhybridized, sigma bond, pi bond, triple bond

02-20

Title	Bonding in Ethane
Caption	Figure 2-20Ethane is composed of two methyl groups bonded by overlap of their sp3 hybrid orbitals. These methyl groups may rotate with respect to each other.
Notes	Each carbon of an ethane molecule has four (4) sigma bonds (single bonds) formed with its four sp3 hybrid orbitals. Three sigma bonds to hydrogen atoms and one of sigma bonds to another CH3. There is free rotation along single bonds.
Keywords	sigma bonds, free rotation

02-20-04UN

Title	Constitutional Isomers
Caption	If you were asked to draw a structural formula for C4H10, either of the following structures would be a correct answer. The same way there are three constitutional isomers of pentane (C5H12), whose common names are n-pentane, isopentane, and neopentane. The number of isomers increases rapidly as the number of carbon atoms increases.
Notes	Constitutional isomers have the same chemical formula but the atoms are connected in a different order. Constitutional isomers have different properties.
Keywords	isomers, constitutional isomers, chemical formula

02-20-07UN

Title	Geometric Isomers: Cis and Trans
Caption	Cis and trans isomers are only one type of stereoisomerism. The study of the structure and chemistry of stereoisomers is called stereochemistry. We will encounter stereochemistry throughout our study of organic chemistry, and Chapter 5 is devoted entirely to this field.
Notes	Stereoisomers are compounds with the atoms bonded in the same order but their atoms have different orientations in space. Cis and trans are examples of geometric stereoisomers and they occur when there is a double bond in the compound. Since there is no free rotation along the carbon-carbon double bond, the groups on these carbons can point to different places in space.
Keywords	stereoisomers, cis, trans, isomers

02-20-20UN

Title	Dipole Moments
Caption	Bond polarities can range from totally nonpolar covalent, through polar covalent, to totally ionic. In the following examples, ethane has a nonpolar covalent C!C bond. Methylamine, methanol, and chloromethane have increasingly polar (C!N, C!O, and C!Cl) covalent bonds. Methylammonium chloride has an ionic bond between the methylammonium ion and the chloride ion.
Notes	Bond polarity increases as the electronegativity of one of the atoms involved in a covalent bond increases. Bond dipole moment is a measure of the polarity of a bond.
Keywords	polar, polarity, bond dipole moment, electronegativity

02-23

Title	Dipole-dipole Interaction
Caption	Figure 2-23Dipole-dipole interactions result from the approach of two polar molecules. If their positive and negative ends approach, the interaction is an attractive one. If two negative ends or two positive ends approach, the interaction is repulsive. In a liquid or a solid, the molecules are mostly oriented with the positive and negative ends together, and the net force is attractive.
Notes	Dipole-dipole interaction affects the physical properties of a compound. The greater the dipole-dipole interaction, the more energy will be required to vaporize or melt the compound, resulting in higher boiling and melting points.
Keywords	polarity, dipole-dipole interaction, boiling point, melting point

02-24

Title	London Dispersion Forces
Caption	Figure 2-24London dispersion forces result from the attraction of correlated temporary dipole moments.
Notes	A temporary dipole moment in a molcule can induce a temporary dipole moment in a nearby molecule. An attractive dipole-dipole interactive results for a fraction of a second.
Keywords	temporary dipole moment, dipole-dipole interaction, London dispersion forces, Van der Waals forces

02-24-01UN

Title	Effect of Branching on Boiling Point
Caption	The boiling points of three isomers of molecular formula C5H12 are given below. The long-chain isomer (n-pentane) has the greatest surface area and the highest boiling point. As the amount of chain branching increases, the molecule becomes more spherical and its surface area decreases. The most highly branched isomer (neopentane) has the smallest surface area and the lowest boiling point.
Notes	Higher surface areas in the molecule are convenient for London dispersion forces. Branching in a molecule will reduce its surface area, decreasing the amount of London dispersion forces. Longer chain hydrocarbons tend to have higher boiling points than their branched isomers because of this reason.
Keywords	surface area, branching, London dispersion forces, dipole-dipole interaction, boiling point

02-25

Title	Hydrogen Bonding
Caption	Figure 2-25Hydrogen bonding is a strong intermolecular attraction between an electrophilic O!H or N!H hydrogen atom and a pair of nonbonding electrons.
Notes	Hydrogen bonding is an intermolecular interaction found in compounds with N-H and O-H bonds. The strong polar bond between the hydrogen and the heteroatom causes the hydrogen to interact with the lone pair(s) of the heteroatom on nearby molecules. The presence of hydrogen bonding will increase the boiling point of the compound because more energy will be required to break this interaction and vaporize the compound. Hydrogen bonding of O-H is stronger than the hydrogen bonding of N-H.
Keywords	intermolecular, polar, hydrogen bond, boiling point

02-26

Title	Polar Solute in a Polar Solvent Dissolves
Caption	Figure 2-26The hydration of sodium and chloride ions by water molecules overcomes the lattice energy of sodium chloride. The salt dissolves.
Notes	The water molecules will surround the sodium and chloride ions effectively dissolving them.
Keywords	lattice energy, dissolve, hydration, solute, solvent

02-27

Title	Polar Solute in Nonpolar Solvent
Caption	Figure 2-27The intermolecular attractions of polar substances are stronger than their attractions for nonpolar solvent molecules. Thus, a polar substance does not dissolve in a nonpolar solvent.
Notes	The solvent cannot break apart the intermolecular interaction of the solute so the solid will not dissolve in the solvent.
Keywords	solute, solvent, polar, nonpolar, intermolecular interaction

02-28

Title	Nonpolar Solute in Nonpolar Solvent
Caption	Figure 2-28The weak intermolecular attractions of a nonpolar substance are overcome by the weak attractions for a nonpolar solvent. The nonpolar substance dissolves.
Notes	The solvent can interact with the solute molecules separating them and surrounding them. This causes the solute to dissolve in the solvent.
Keywords	solute, solvent, polar, nonpolar, intermolecular interaction

02-29

Title	Nonpolar Solute in Polar Solvent
Caption	Figure 2-29If a nonpolar molecule were to dissolve in water, it would break up the hydrogen bonds between the water molecules. Therefore, nonpolar substances do not dissolve in water.
Notes	Hydrogen bonding is a much stronger interaction than the interaction between a nonpolar solute and water so it is difficult for the solute to break apart the water molecules. Therefore a nonpolar solute will not dissolve in water.
Keywords	hydrogen bond, polar, nonpolar, solute, solvent

02-29-03T2-2

Title	Prefixes and Number of Carbon Atoms
Caption	TABLE 2-2ÊCorrespondence of Prefixes and Numbers of Carbon Atoms
Notes	Alkanes have the -ane suffix and the number of carbons in the molecule is specified by a prefix. For example the prefix meth- represents one carbon, so methane is an alkane of only one carbon of CH4.
Keywords	prefix, suffix, alkane

02-31

Title	Naming Alkyl Groups
Caption	Figure 2-31Alkyl groups are named like the alkanes they are derived from, with a -yl suffix.
Notes	The alkyl substituents on an alkane are named using the same prefixes to specify the number of carbons and adding the -yl suffix to specify that it is a branch on a main alkane.
Keywords	alkyl, branch, suffix

02-31-02UN

Title	Naming Alkenes
Caption	CarbonÐcarbon double bonds cannot rotate, and many alkenes show geometric (cis-trans) isomerism (Section 2-10). The following are the cis-trans isomers of some simple alkenes:
Notes	Alkenes have the -ene suffix and the number of carbons in the molecule is specified by a prefix. Thus, ethene is an alkene with two carbon atoms. The position of the double bond is specified by a number while the geometry of the double bond is specified by using cis or trans in front of the alkene name.
Keywords	alkene, geometric isomer, cis, trans

02-31-12UN

Title	Alcohols
Caption	Alcohols are among the most polar organic compounds because the hydroxyl group is strongly polar and can participate in hydrogen bonding. Some of the simple alcohols like ethanol and methanol are miscible (soluble in all proportions) with water. Four of the most common alcohols are given below. Notice that the suffix of each name is the -ol suffix from the word Òalcohol.Ó
Notes	Alcohols are named by using the suffix -ol after the prefix specifying the number of carbons in the molecule. The location of the OH groups has to be specified in the name, thus, 2-propanol has the OH attached to the second carbon of the chain.
Keywords	alcohol

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