资源描述
Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,1.7Structural Formulas of Organic Molecules,1.7Structural Formulas of Org,Constitution,The order in which the atoms of a molecule are connected is called its,constitution,or,connectivity,.,The constitution of a molecule must be determined in order to write a Lewis structure.,ConstitutionThe order in which,Step 1: The molecular formula and the connectivity are determined by experiment.,Table 1.4 How to Write Lewis Structures,Step 1: The molecular formul,Step 1: The molecular formula and the connectivity are determined by experiment.,Example:Methyl nitrite has the molecular formula CH,3,NO,2,. All hydrogens are bonded to carbon, and the order of atomic connections is CONO.,Table 1.4 How to Write Lewis Structures,Step 1: The molecular formul,Step 2: Count the number of valence electrons. For a neutral molecule this is equal to the number of valence electrons of the constituent atoms.,Table 1.4 How to Write Lewis Structures,Step 2: Count the number of,Step 2: Count the number of valence electrons. For a neutral molecule this is equal to the number of valence electrons of the constituent atoms.,Example (CH,3,NO,2,):Each hydrogen contributes 1 valence electron. Each carbon contributes 4, nitrogen 5, and each oxygen 6 for a total of 24.,Table 1.4 How to Write Lewis Structures,Step 2: Count the number of,Step 3: Connect the atoms by a covalent bond represented by a dash.,Table 1.4 How to Write Lewis Structures,Step 3: Connect the atoms by,Step 3: Connect the atoms by a covalent bond represented by a dash.,Example:Methyl nitrite has the partial structure:,Table 1.4 How to Write Lewis Structures,C,O,N,O,H,H,H,Step 3: Connect the atoms by,Step 4: Subtract the number of electrons in bonds from the total number of valence electrons.,Table 1.4 How to Write Lewis Structures,C,O,N,O,H,H,H,Step 4: Subtract the number,Step 4: Subtract the number of electrons in bonds from the total number of valence electrons.,Example:24 valence electrons 12 electrons in bonds. Therefore, 12 more electrons to assign.,Table 1.4 How to Write Lewis Structures,Step 4: Subtract the number,Step 5: Add electrons in pairs so that as many atoms as possible have 8 electrons. Start with the most electronegative atom.,Table 1.4 How to Write Lewis Structures,Step 5: Add electrons in pai,Step 5: Add electrons in pairs so that as many atoms as possible have 8 electrons. Start with the most electronegative atom.,Example:The remaining 12 electrons in methyl nitrite are added as 6 pairs.,Table 1.4 How to Write Lewis Structures,.,C,O,N,O,H,H,H,.,.,:,.,.,Step 5: Add electrons in pai,Step 6: If an atom lacks an octet, use electron pairs on an adjacent atom to form a double or triple bond.,Example:Nitrogen has only 6 electrons in the structure shown.,Table 1.4 How to Write Lewis Structures,.,C,O,N,O,H,H,H,.,.,:,.,.,Step 6: If an atom lacks an,Step 6: If an atom lacks an octet, use electron pairs on an adjacent atom to form a double or triple bond.,Example:All the atoms have octets in this Lewis structure.,Table 1.4 How to Write Lewis Structures,.,.,C,O,N,O,H,H,H,.,:,.,Step 6: If an atom lacks an,Step 7: Calculate formal charges.,Example:None of the atoms possess a formal charge in this Lewis structure.,Table 1.4 How to Write Lewis Structures,.,.,C,O,N,O,H,H,H,.,:,.,Step 7: Calculate formal cha,Step 7: Calculate formal charges.,Example:This structure has formal charges; is less stable Lewis structure.,Table 1.4 How to Write Lewis Structures,.,.,C,O,N,O,H,H,H,.,:,.,+,Step 7: Calculate formal cha,Condensed structural formulas,Lewis structures in which many (or all) covalent bonds and electron pairs are omitted.,H,O,C,C,C,H,H,H,H,H,H,:,:,H,can be condensed to:,CH,3,CHCH,3,OH,(CH,3,),2,CHOH,or,Condensed structural formulasL,Bond-line formulas,Omit atom symbols. Represent structure by showing bonds between carbons and atoms other than hydrogen.,Atoms other than carbon and hydrogen are called,heteroatoms,.,CH,3,CH,2,CH,2,CH,3,is shown as,CH,3,CH,2,CH,2,CH,2,OH,is shown as,OH,Bond-line formulasOmit atom sy,Bond-line formulas,Omit atom symbols. Represent structure by showing bonds between carbons and atoms other than hydrogen.,Atoms other than carbon and hydrogen are called,heteroatoms,.,H,Cl,C,C,H,2,C,H,2,C,CH,2,CH,2,H,H,is shown as,Cl,Bond-line formulasOmit atom sy,1.8Constitutional Isomers,1.8Constitutional Isomers,Constitutional isomers,Isomers are different compounds that have the same molecular formula.,Constitutional isomers are isomers that differ in the order in which the atoms are connected.,An older term for constitutional isomers is “structural isomers.”,Constitutional isomersIsomers,A Historical Note,In 1823 Friedrich Whler discovered that when ammonium cyanate was dissolved in hot water, it was converted to urea.,Ammonium cyanate and urea are constitutional isomers of CH,4,N,2,O.,Ammonium cyanate is “inorganic.” Urea is “organic.” Whler is credited with an important early contribution that helped overturn the theory of “vitalism.”,NH,4,OCN,Ammonium cyanate,H,2,NCNH,2,O,Urea,A Historical NoteIn 1823 Frie,Nitromethane,Methyl nitrite,.,:,H,C,O,O,N,:,:,.,+,H,H,Examples of constitutional isomers,Both have the molecular formula CH,3,NO,2,but the atoms are connected in a different order.,.,C,O,N,O,H,H,H,.,:,.,.,NitromethaneMethyl nitrite.:H,1.9Resonance,1.9Resonance,two or more Lewis structures may be written for certain compounds (or ions),Resonance,two or more Lewis structures m,Step 6: If an atom lacks an octet, use electron pairs on an adjacent atom to form a double or triple bond.,Example:Nitrogen has only 6 electrons in the structure shown.,Table 1.4 How to Write Lewis Structures,.,C,O,N,O,H,H,H,.,.,:,.,.,Step 6: If an atom lacks an,Step 6: If an atom lacks an octet, use electron pairs on an adjacent atom to form a double or triple bond.,Example:All the atoms have octets in this Lewis structure.,Table 1.4 How to Write Lewis Structures,.,.,C,O,N,O,H,H,H,.,:,.,Step 6: If an atom lacks an,Step 7: Calculate formal charges.,Example:None of the atoms possess a formal charge in this Lewis structure.,Table 1.4 How to Write Lewis Structures,.,.,C,O,N,O,H,H,H,.,:,.,Step 7: Calculate formal cha,Step 7: Calculate formal charges.,Example:This structure has formal charges; is less stable Lewis structure.,Table 1.4 How to Write Lewis Structures,.,.,C,O,N,O,H,H,H,.,:,.,+,Step 7: Calculate formal cha,same atomic positions,differ in electron positions,more stable Lewis structure,less stable Lewis structure,.,.,C,O,N,O,H,H,H,.,:,.,+,.,.,C,O,N,O,H,H,H,.,:,.,Resonance Structures of Methyl Nitrite,same atomic positionsmore stab,same atomic positions,differ in electron positions,more stable Lewis structure,less stable Lewis structure,.,.,C,O,N,O,H,H,H,.,:,.,+,.,.,C,O,N,O,H,H,H,.,:,.,Resonance Structures of Methyl Nitrite,same atomic positionsmore stab,Electrons in molecules are often delocalizedbetween two or more atoms.,Electrons in a single Lewis structure are assigned to specific atoms-a single Lewis structure is insufficient to show electron delocalization.,Composite of resonance forms more accurately depicts electron distribution.,Why Write Resonance Structures?,Electrons in molecules are of,Ozone (O,3,),Lewis structure of ozone shows one double bond and one single bond,Expect: one short bond and one long bond,Reality: bonds are of equal length (128 pm),Example,O,O,O,+,Ozone (O3)Expect: one short b,Ozone (O,3,),Lewis structure of ozone shows one double bond and one single bond,Resonance:,Example,O,O,O,+,O,O,O,+,O,O,O,+,Ozone (O3)Resonance:ExampleOO,
展开阅读全文