Organic Chemistry Solomon and Fryhle: Ch2 Representative Carbon Compounds

POLAR, NON-POLAR MOLECULES

• Non-polar covalent bonds have no difference in electronegativity between bonded atoms ie. No charge separation. 
• Ex. H2, Cl2, O2, N2….
• Polar covalent bonds have a difference in electronegativity between atoms in which the center of the positive charge and the negative charge coincide, so no  net dipole moment is created.
• The overall polarity is the sum of all the dipole vectors.

PHYICAL PROPERTIES AND MOLECULAR STRUCTURE

• The physical properties include melting point, boiling points, density, dipole moment, and solubility.
• Intermolecular forces (van der waals) - these are forces that act between molecules that give them the ability to exist in liquid and solid states even though they are non-polar.
• Dipole - a movement resulting in a non-uniform distribution of bonding electrons. This will cause the molecules to orient themselves so that the positive end of one molecule is directed toward the negative end of another. 
• This is also apparent in Cis (same) and Trans (opp) alkenes which have different physical properties.

 

• Hydrogen bonds - a very strong dipole-dipole bond that occurs between a hydrogen and a small, or strongly electronegative atom (O,N, or F) and other non bonding electron pairs. These are stronger than dipole bonds but weaker than covalent bonds.
• Dispersion forces - (London force) this is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This is the force that causes non-polar substances to change from liquid to solids when the temp is lowered significantly.
• Symmetry - molecules that are symmetrical tend to have abnormally high melting points due to the compactness of the molecule.
• Solubility - a solvent will only be soluble in its solute if the molecules of the solute are able to overcome the intermolecular forces that are holding the solvent in its solid state.     
• Polar compounds - these are soluble only by water and a few other solutes, they do so by hydrating or solvating the ions.
• Like dissolves like
• Some alkyl groups are miscible in water though, namely methanol and ethanol due to their short carbon chains. Since they are more like water than an alkane they will dissolve in water, but if there is a long carbon chained alcohol it will not dissolve in water because its carbon chain makes it more like an alkyl than an alcohol.
• 1-3carbons are soluble in water
• 4-5 carbon chains are borderline
• 6 or more carbons are not soluble in water.
• Changes from order to disorder are favorable, but changes from disorder to order are not favorable.  

CARBON-CARBON BONDS

• Carbon has a unique bonding ability with other atoms (H, O, N, S, and halogens)
• Carbon compounds have a very large number of possible compounds that allow for a great deal of complexity and many many isomers.

HYDROCARBONS

• These molecules contain only carbon and hydrogen
• Alkanes - single carbon-carbon bonds
• Ethane (also called acetylene)

 

• Alkenes - have at least one carbon-carbon double bond (planer in shape)

 

• Alkynes - have at leave one carbon-carbon triple bond ( this will have a linear shape)

 

• Aromatic hydrocarbons - (benzene rings)  these are sp2 hybridized

 

FUNCTIONAL GROUPS

• This is where most of the chemical reactions will take place.  
• Alkyl halides - compounds in which a halogen atom replaces a hydrogen atom of an alkane (halo alkanes). These can be divided into groups depending on the number of carbons that its attached carbon is attached to ( 1°, 2°, 3°)

• Alcohols - (methanol/ethanol) have the structural form CH3OH, characterized by its hydroxyl (OH) group attached to an sp3 carbon.

• Ethers- these have the general formula of R-O-R or R-O-R' (where R' may be an alkyl or phenyl group different from R). These can be thought of as water where the hydrogen atoms have been replaced by alkyl groups. One way we name these is by naming the attached alkyl groups (diethyl ether)

• Amines - can be thought of as derivatives of ammonia (NH3). This is classified depending on the number of carbon (organic groups) that are attached to the nitrogen.  This is also an sp3 hybridization.

• Carbonyl group - a group in which a carbon is double bonded to an oxygen.

• Ketone - this is a carbonyl group that is bonded to two carbon atoms (RCOR or RCOR') has a trigonal planer arrangement.

• Aldehydes - a carbonyl group that is bonded to one hydrogen and one carbon atom ( RCHO or HCHO) has a trigonal planer arrangement. 

• The following groups of carboxylic acids, esters, and amides can be inter converted using chemical reactions that will be covered later.
• Carboxylic acids - a carbonyl and hydroxyl group combined with the general formula of RCO2H or RCOOH. Examples of these are formic acid, acetic acid, and benzoic acid.

 

• Esters - have the general formula RCO2R' or RCOOR', where a carbonyl  group is bonded to an alkoxyl group.

 

•  Esters can be made from a carboxylic acid and an alcohol through the acid catalyzed loss of a molecule of water, which the OH of the acid will react with the Hydrogen of the alcohol. This will then allow for the remaining portion of the alcohol to attach to the remaining portion of the acid.
• Amides - a carbonyl group is bonded to a nitrogen atom bearing hydrogen and/or alkyl groups with the general formula RCONH2 or RCONHR'.

 

COMMON ORGANIC TERMINOLOGY

• Alkyl groups "R-"
• The dash show attachment to the rest of the molecule.
• IUPAC names

• Methyl is one carbons, ethyl has 2 carbons, and propyl has 3 carbons… isopropyl groups have 3 carbons that are not in a chain. Each lower group can derived from the groups above it.
• When a carbon ring is attached to some other groups, it is called a phenyl. The phenyl group and its CH2 group attaching it to the rest of the molecule makes up the benzyl group.

• Sub-classification of Sp3 carbons atoms
• 1°, 2°, 3° alkyl halides
• Primary carbons are bonded to one other carbon
• Secondary carbons are bonded to two other carbons
• Tertiary carbons are bonded to three other carbons
• Quaternary carbons are bonded to four other carbons
• Classification of alkyl halides (-X)  and alcohols (-OH)
• Can either be primary, secondary, or tertiary
• The degree here is determined by how many carbons are attached to the carbon that the halide or alcohol is bonded to
• Classification of Amines
• Primary, secondary, or tertiary possibilities
• This is dependent on how many carbons the Nitrogen is bonded to, meaning this focuses on the nitrogen and not the carbon as the center atom.

CURVED ARROWS

• A curved arrow is used to show the movement of electrons in a Lewis Structure 
• The arrow needs to starts where the electron was originally (either a bond or lone pair) then ends where the electron is being moved to.

 

• Do not move an atom from a positively charged atom, and do not go from an atom to a lone pair ( this would suggest that the atom moved.
• Homolysis - the bond is evenly broken, this produces fragments with unpaired electrons called radicals.

 

• Heterolysis - the bond is not evenly broken, one will get both electrons while the other will get none ( this will depend on electronegativity, where the bond is polarized) this will form charged fragments or ions.

• Making bonds
• Coordinate covalent bonds - where one atom brings two electrons to the bond while the other brings none; it doesn’t matter where the electrons are coming from just that they are there.

 

• An arrow can also be used to show electron flow during a chemical reaction.
• Curved arrows can also help depict resonance structures.

IR SPECTRA

• This is used to identify functional groups, which will absorb at different frequencies, showing the IR spectra
• When a bond absorbs IR, it will stretch or bend changing the average amplitude of the bond but not the frequency of the vibration. This absorption is due to how strong the bond is and the size of the atoms.
• The frequency is equal to the IR absorption. A stronger bond will absorb more energy, as will a lighter atom.