hapter 2 Molecular Representations
Structural Formulas and ondensed Structures Because organic compounds are molecular in nature, the additional information conveyed in structural formulas is sometimes necessary. Structural formulas show the connections between atoms based on their abilities to form covalent bonds. F l Br
Structural Formulas and ondensed Structures Because certain carbon and hydrogen groupings are so common, some abbreviations are used. 3 2 2 2 ( 2 ) 2
Structural Formulas and ondensed Structures Abbreviations for yclic Structures 2 2 2 2 2 2 612 2 2 2 2 2 2 2 2 1018 66
Ways of Depicting Formulas and Models of an Alkane 3 3 3 3 3 2 3 2 3 3 3 2 3 2 2 3 3 2 920
Give molecular formulas for the following compounds. Line structure idden hydrogens revealed 3 3 3 716 3 3 910 76
hemical Formulas and Unsaturation n n 2n n 2n+2 n 2n+2
hemical Formulas and Unsaturation n n n n n 2n n 2n
hemical Formulas and Unsaturation ydrocarbons Saturated ydrocarbons Unsaturated ydrocarbons Alkanes n2n+2 ycloalkanes n2n (one ring) Alkenes n2n (one =) Alkynes n2n-2 (one ) Benzene 66 n2n-6
Structural Formulas and ondensed Structures Example of a ondensed Structure: What does the molecular formula 1122 represent? 3 3 3 ( 2 ) 4
Rules concerning line structures: 1. Draw single-bonded carbons in a zig-zag manner. 2. Draw multiple bonds with correct geometry. 3. Direction of single bonds is irrelevant. 4. eteroatoms and hydrogens attached to heteroatoms must be included. 5. arbon can have no more than four bonds.
Functional Groups Functional group - A characteristic group of atoms and bonds that imparts particular physical and chemical properties on a molecule.
Families of rganic ompounds Alkanes Aldehydes Alkenes Ketones Alkynes arboxylic Acids Aromatics Esters Alcohols Amines Ethers Amides
Functional Groups
Functional Groups 2 3 S P P Acetyl oa P
2 3 S P P P Acetyl oa
3. Identify the major functional groups in the following molecules. 2 2 alcohol (phenol) amine carboxylic acid 3 ester amine ester amine ether
Bonds pointing backward Bonds pointing toward the observer Bonds in the plane of the screen Representation of Bonds in Three Dimensions
Representation of Bonds in Three Dimensions (S)-carvone caraway (R)-carvone spearmint
Resonance Structures Resonance structures - A series of structures which collectively represent a single entity with delocalized electrons.
The Use of urved Arrows to Show Movement of a Pair of Electrons Tail to ead Movement Source of Electrons a lone pair or a bond An electron donor Destination of Electrons a positive charge or an atom lacking an octet An electron acceptor
Formations of Allyl ation 2 3 2 2 + :- +
Formations of Allyl ation or or + +
Resonance of Allyl ation + +
Representing Resonance Structures Moving Electrons
Moving Electrons The three legal moves of resonance: 1) Two π bond electrons lone pair 2) Lone pair of electrons π bond 3) Two π bond electrons π bond
Moving Electrons Two illegal moves for the formation of resonance structures: 1) Breaking single bonds + 3 + 2) Exceeding octets for second-row elements
Representing Resonance resonance hybrid allyl cation: acetate anion: 3 3 3 benzene molecule:
4. Draw the resonance form of the structure resulting from the given movement of electrons. 2 2
5. Insert arrows to interconvert the following resonance forms. 3 3 3 2 3 2 2 2 2 2 2 2
hapter 2 Resonance Structures Formal harges
ommon Bonding Patterns B F + + + F + B F
Formal harges on xygen 1 bond + 3 lone pairs no net charge 2 bonds + 2 lone pair 3 bonds + 1 lone pair
2 bonds + 2 lone pairs no net charge 3 bonds + 1 lone pair 4 bonds + 0 lone pairs Formal harges on itrogen
Formal harges on arbon 3 bonds + 1 lone pair no net charge 4 bonds + 0 lone pairs 3 bonds + 0 lone pairs
Resonance Structures Pattern Recognition
Five Patterns for Resonance Structures Allylic lone pair Allylic positive charge Lone pair adjacent to positive charge pi bond between two atoms of differing electronegativity onjugated pi bonds enclosed in a ring Two curved arrows ne curved arrow ne curved arrow ne curved arrow Three curved arrows
Resonance stabilization - The stabilization associated with the delocalization of electrons via resonance.
Resonance Structures Assessing the Importance of Structures 1. umber of charges should be minimized. 2. ighly electronegative atoms can bear a charge if they possess an octet of electrons. 3. Two adjacent carbons should not bear opposite charges.
Assessing the Importance of Structures 0 charges significant 2 charges insignificant
Assessing the Importance of Structures 1 charge significant 1 charge significant 3 charges insignificant 3 charges insignificant
Assessing the Importance of Structures 3 charges insignificant 1 charge significant 1 charge significant
Assessing the Importance of Structures Both significant