OCHEM 1 REVIEW SHEET ESSENTIAL INFORMATION ONLY Chapter 1 Basics How bonds form duh Functional groups also duh Lewis structure review o Try to minimize formal charge and put charges on appropriate electronegative atoms o Resonance Use double sided arrows to show resonance between structures Real structure is some intermediate between the resonance forms so there may be dispersed partial charges Never break a sigma bond to make a new resonance structure Having an octet takes precedence over minimizing formal charges Bonding is the result of electron wave particle theory o Energy of electrons differ proportional to the wave function Greatest probability of location of electron is its orbital o Bonds occur when constructive overlap of wave functions occur additive effect Antibonding occurs when waves are destructive not in sync For every orbital there is one bonding orbital and one antibonding orbital of higher energy If antibonding orbital is filled it will cancel any bonding To make orbitals of equal energy we create hybrid orbitals o May bump up electron from s orbital to p orbital to create uniform distribution of electron density then create hydridized orbitals Possible to do so because we can add the wave functions o Sp3 sp2 sp orbitals More p means longer bond weaker bond more s character is stronger bond closer to nucleus greater effective nuclear charge Also helps minimize electron electron repulsion Remember geometry tetra 109 trig pyr 107 bent 103 Lone pairs will reside in a hybrid orbital if present to minimize repulsion Chapter 2 Acid Base Acid dissociation constant Ka is K eq o H2O is on both sides of the equation so it cancels out o A large Ka means that it is a strong acid Ka for water is 10 16 107 2 density of water 55 5 o pKa is logKa a simpler way of communicating constant as pKa increases acidity decreases o Key pKa s to know alkanes 50 alkenes 42 alkyne 24 NH3 38 Alcohols 18 H2O 16 HCOOH 5 HCl 7 period Determining the best conjugate base is easy way to predict reaction direction o Should be most electronegative atom with neg charge more stable when going across o When going down a column larger polarizable atoms are better as outermost e shell is large and can easily accept another e o If applicable more stable base has the most s character in its orbitals variation on more electronegative because closer to the nucleus o Resonance distributes negative charge so better o Large e withdrawing groups have inductive effects that also stabilizes negative charge o Could also use pKa argument more stable conjugate base has the acid that has lower pKa run away from low pKa in reaction Bronsted Lowry acid base o Acids donate protons bases accept protons Lewis acid base o Acids accept electrons bases donate electrons Chapter 3 Alkanes Naming alkanes Physical properties o Physical state at RT o Use base name derived from number of carbon weird ones are undecane dodecane tridecane tetradecane pentadecane icosane 20 Some common names to know isopropyl isobutyl sec butyl t butyl o Halogens are put in front of base with defining position o To name Find largest carbon chain this is your base Number substituents to minimize total sum and give priority to proper groups add substitutions in alphabetical order to name iso and cyclo prefixes are the only ones that count towards naming C1 C4 are gases C5 C20 are liquids C20 are solids Increased carbons means molecule have greater surface area resulting in more potential van der waals forces as the result of dipole moments random dipoles made from e movement o Combustion o Boiling points Reacts with oxygen when heated to produce carbon dioxide and water State of alkane will alter reaction rate To vaporize must interrupt the van der waals interactions So more surface area higher boiling point Branched alkanes will have lower boiling point than straight alkanes of the same size o Melting point o Solubility Dependent entirely on how well a molecule can form a crystal lattice More symmetrical and condensed alkanes branching allows for tighter packing so they have a higher melting point Straight alkanes can t really pack together that tightly think a stack of paper so have a lower melting point Highly dependent on the polarity and dipole moments of the molecule Water is polar has permanent dipole Alkanes are nonpolar but have dipole moments o Without the dipole they are not soluble in the polar solvents because there are no attractions between nonpolar and polar molecules o The temporary dipoles may result in slight negligible solubility Conformational analysis o Looking down an atom s bonds through Newman Projections o C C single bonds allow for free rotation around a bound Therefore attachments can revolve around the carbon in space This allows for different confirmations called conformers Not seen in double bonds because they lack free rotation Staggering the attached bonds to the carbons ie they don t overlap creates the more stable staggered conformer Minimize e e repulsion Overlapping bonds results is less stable eclipsed conformer o Of a higher energy state than the staggered conformer o Conversion between conformers requires energy Barrier to free rotation caused when 2 sigma bonds try to pass each other is called torsional strain Typically this barrier can be overcome because it is very small and RT provides enough energy about 17 20 kcals available for use o Larger molecules with lots of large groups cause steric strain This is the e e repulsion caused when two large groups like two methyls try to occupy the same space ie overlap Therefore the most stable conformer is the anti conformer which is staggered to minimize steric crowding This places the two largest substituents in the Newman Projection in opposite positions When the two largest substituents are approaching eclipsed conformer this is called the gauche conformer there are two one for either side of eclipsed o When drawing Newman projections always rotate one carbon while keeping the other carbon stationary This is to just make sure you don t lose track of what goes where Chapter 3 Predicting Reactions with Alkanes Types of chemical reactions o Homolytic Radical or free radical reactions in which a bond is broken up equally amongst two atoms creating 2 radicals with a free e Drawn as two one sided arrows splitting electrons equally to both o Heterolytic atoms Ionic reactions in which one atom in a bond takes all the electrons with it when the bond breaks creating a