Organic Chemistry- Exam 1

Organic Chemistry- Exam 1(2023) the naming of organic compounds has three parts - 1) parent name- indicates the number of carbons in the longest continuous chain 2) suffix- indicates what functional group is present 3) prefix- tells us identity, location, and number of substituents attached to the carbon chain prefix + parent + suffix octet rule - -all group A elements (except H and He) desire to have 8 electrons in their valence shell -elements will make bonds to satisfy this rule duet rule - -H and He -when the valence shell of H an He is filled, there are only two electrons how are the halogens able to obey the octet rule - -F, Cl, Br, I 1) they form ions 2) form a covalent bond carbon - -only have 4 valence electrons- do not obey the octet rule -carbon atoms are not practical because it cannot steal 4 valence electrons, easily -covalent bonds aren't a problem (single, double, triple, C--H, C--O) complete structures - - ALL bonds and ALL atoms are shown condensed structures - -all atoms drawn in, but bond lines are generally omitted -atoms are drawn next to atoms they are bonded to -lone pairs omitted -ex) CH4 skeletal structure - -you assume there is a carbon atom at the junction of any two lines, or at the end of any line -assume there are enough hydrogens around each C molecular shape- bond angle - -bond angle determines the shape around any atom bonded to two other atoms two groups= linear (180) three groups= trigonal planar (120) four groups= tetrahedral (109.5) tetrahedral three dimensional structure - -the molecule is not planar -wedge indicates a single bond orientated toward you -dashed line indicates a single bond directed away from you -solid line is used for a bond in the plane why does carbon form so many varieties of covalent bonds? - -valence electrons and bonds of C dictate what the overall shape and structure of the molecule is -shape and structure dictates the physical and chemical properties of the molecule Ex) barbituric acid- one structure causes hypnotic activity, the other is used to prevent seizures atoms - -the electrons of atoms reside in shells first shell - -closest to nucleus -contains 2 electrons max -reside in s orbital (1s) second shell - -a little farther from nucleus -contains 8 electrons max -these electrons are the basis of the octet rule -reside in one s orbital and three p orbitals (2s, 2px, 2py, 2pz) -max of 2 electrons can go in each orbital s orbital - -sphere -lower in energy p orbital - - dumbbell shape -contains node of electron density at the nucleus -higher in energy than s orbital covalent bonds - -form when an orbital contains only 1 electron -this unfilled orbital contacts another orbital that has a single electron in it -two orbitals merge and share their electrons carbon- orbital - -has two core electrons -four valence electrons -electrons are placed in the orbitals of lowest energy, to highest -carbon has two in the 2s orbital and one each in 2p orbitals -this makes means carbon should form only 2 bonds, making it a very unstable molecule carbon- orbital: possible solution - -promotion of an electron from 2s to a vacant 2p orbital -forms four unpaired electrons for bonding -this is still not adequate: carbon would form two different types of bonds (evidence shows it forms four identical bonds) carbon- orbital: solution - -atoms like carbon do not use pure s and p orbitals, they use a set of new, hybrid, orbitals -sp3 hybridization= 109.5 degrees hybridization - -the combination of two or more atomic orbitals to form the same number of hybrid orbitals, each having the same shape and energy hybrid s orbitals - -hybrid s orbitals form sigma covalent bonds, whose electrons are submerged hybridization for carbons forming double bonds - -ethylene= each carbon is bonded to 3 atoms, therefore we only need 3 hybrid orbitals -average the 2s orbital with two 2p orbitals to get three sp2 hybrid orbitals -sp2 hybridization= 120 degrees p electrons - -p electrons form pi covalent bonds, whose electrons are on the periphery (exposed) sigma vs pi - -sigma= you have only single bonds -pi= double or triple bonds bond angle tells you hybridization - 180 degrees= sp hybridization 120 degrees= sp2 hybridization 109.5 degrees= sp3 hybridization bond length: single, double, triple C-C bonds - -the distance between the two C atoms is different for the 3 groups shortest= triple bond middle= double bond longest= single bond -as the number of electrons between to nuclei increases, bonds become shorter, and stronger the reason behind bond length difference - -you have to look at the difference between hybrid orbitals -the shortest= sp; 50/50 s to p ratio -middle= sp2; 33% s, 67% p