Formal Charge Worksheet / Chem 314 Beauchamp

Formal Charge – a convention designed to indicate an excess or deficiency of electron density compared to an atom’s neutral allocation of electrons.

Formal electrons in 1 electrons in Charge =Zeffective lone pairs 2 covalent bonds

This number never changes for an atom and represents positive Total valence electrons allocated to an atom charge not cancelled assuming electrons are shared evenly in bonds. by core electrons. This number varies depending on the bonding arrangement. It is negative because electrons are negative. Rules of Formal Charge

1. When an atom’s total valence electron credit exactly matches its Zeff, there is no formal charge.

2. Each deficiency of an electron credit from an atom’s normal number of valence electrons produces an additional positive charge.

3. If the formal charge calculation shows excess electron credit over an atom’s normal number of valence electrons, a negative formal charge is added for each extra electron.

4. The total charge on an entire molecule, ion or free radical is the sum of all of the formal charges on the individual atoms.

Write 3D structures for all resonance contributors. Rank them from best (=1) to last. Judge your structures on the basis of 1. maximum number of bonds / full octets, 2. minimize formal charge, 3, consistent formal charge based on electronegativity.

Cations a. b. c. d. e. f. H COH 2 H2CNH2 (CH3)2COH (CH3)2CNHCH3 (CH3)2CCH2CH3 H2CCOH 2 resonance 2 resonance 2 resonance 2 resonance 2 resonance structures structures structures structures structures g. h. i. j. k. l. HC(OH) HC(NH )(OH) HC(NH ) 2 2 2 2 HC(OCH3)(OH) H2CCHCH2 H2CCCH 3 resonance 3 resonance 3 resonance 3 resonance 2 resonance 2 resonance structures structures structures structures structures structures

m. n. Anions p. q. r. s. HCO HCNH o. H2CCHO H2CCHNH H2CCN H2CCHCH2 H2CCCH 2 resonance 2 resonance 2 resonance 2 resonance structures 2 resonance 2 resonance 2 resonance structures structures structures structures structures structures

y:\files\classes\0 Organic Topics - latest\315 topics\20 315 lecture notes, 7-9-15\314 Review Problems\04 formal charge, 2D, resonance, probs & answers, 6p.doc Formal Charge Worksheet / Chem 314 Beauchamp Possible answers

a b c d e H H H H H H f H H H O N C H O N H O H C H H C H H C C H C H C C C C C C C C H C H H H H H H H H H H H H H H H H H

H H H H H H O N O N O H C H H C H H C H C C C C C C C H H H H H H H H H H H H H

g h i k H H H H H j H H l O N N O H H H H C H C C H C H C H C C C C H C H O H O H N H O H C H H H H

H H H H H H H H C O N N O H H C H H C H C C C C H C H C H C C H O H N H O H H O H H H H

H H H H H H O N N O H H C H C H C H C C H O H O H N H O H

H

H q H m n o O N rsH H p N O H C C N H C H C H C C H C C H C C C H C H C H C H H H H H H H

H H O N H H O N N C C H C C H C H C H C H H C H C H C H C H C C C

H H H H H H

y:\files\classes\0 Organic Topics - latest\315 topics\20 315 lecture notes, 7-9-15\314 Review Problems\04 formal charge, 2D, resonance, probs & answers, 6p.doc Formal Charge Worksheet / Chem 314 Beauchamp Write formal charge next to the atom with the charge, if present.

H H H H H H H C H H C H C H C H C H C

H H H H

H H H

H N H H N H N H N N H H

H H

H O H H O H O H O O

H

H F H F F F

H H H H H

CC CC CCH CCH H C C H

H H H H H H

H C C H C N H H C N CN H C O

O H O O O H C H C CO C C H H C C H H H C H H H H H

H H H H O H N N N O H C H C H C H C C H H C C H C H C H C H H H H H H H H H y:\files\classes\0 Organic Topics - latest\315 topics\20 315 lecture notes, 7-9-15\314 Review Problems\04 formal charge, 2D, resonance, probs & answers, 6p.doc Formal Charge Worksheet / Chem 314 Beauchamp

Possible answers H H H H H H H C H H C H C H C H C H C

H H H H

H H H -2 -3 H N H H N H N H N N H H

H H -2 H O H H O H O H O O

H

H F H F F F

H H H H H

CC CC CCH CCH H C C H

H H H H H H

H C C H C N H H C N CN H C O

H O O O O H C H C CO C H C C H C H H H C H H H H H

H H H H O H N N N O H C H C H C H C C H H C C H C H C H C H H H H H H H H y:\files\classes\0 Organic Topics - latest\315 topics\20 315 lecture notes, 7-9-15\314 Review Problems\04 formal charge, 2D, resonance, probs & answers, 6p.doc Formal Charge Worksheet / Chem 314 Beauchamp Add in any resonance details and write formal charge next to the atom with the charge, if present. a. b. c. d. e. f. CO -2 CH3NO2 CH2N2 NH3CH2CO2 CH3N3 3 C(NH2)3 g. i. j. h. k l -2 NO N CO2 SO 2 3 2 SO3 SO3

p q m -2 n o r C H CH SO NO2 NO3 6 5 2 C6H5CH2 C6H5CH2 4

Possible answers

a. CH3NO2 b. CH2N2 H H O O H H H C N H C N C N N C N N O H O H H H

c. NH3CH2CO2 d. CH3N3

H H O H H O H H

H N C C H N C C H C N N N H C N N N

H H O H H O H H

-2 e. CO3 f. C(NH2)3

O O NH O NH2 NH2 2

C C C C C C O O O O H N NH O O H2N NH2 H2N NH2 2 2

g. h. N NO2 3 -2 -2 O N O O N O O N O N N N N N N N N N

i. CO2 j. SO2 O O O O C O O C O O C O O S O S O S

-2 k SO3 l SO3 O O several O O O other ways S S to show S S S O O resonance O O O O O O O O

y:\files\classes\0 Organic Topics - latest\315 topics\20 315 lecture notes, 7-9-15\314 Review Problems\04 formal charge, 2D, resonance, probs & answers, 6p.doc Formal Charge Worksheet / Chem 314 Beauchamp -2 m SO4 n NO2 O O several O O other ways O S O O S O to show O N O N resonance O O

O O o NO3 O

N N N O O O O O O

p CH CH 2 CH2 CH2 2

q

CH2 CH CH2 CH2 2

r CH CH2 CH2 CH2 2

y:\files\classes\0 Organic Topics - latest\315 topics\20 315 lecture notes, 7-9-15\314 Review Problems\04 formal charge, 2D, resonance, probs & answers, 6p.doc