Organic Chemistry Practice Exam 1

10) Draw condensed structures for the four compounds with formula C3H9N.

Answer: CH3CH2CH2NH2 CH3CH2NHCH3 (CH3)2CHNH2 (CH3)3N

Draw the structure of a molecule which contains only carbon and hydrogen atoms (only three of which are carbon) and in which two of the carbons are sp2 hybridized and the other is sp hybridized.

Answer: H2C=C=CH2

17) Both sigma (σ) and pi (π) bonds can be formed by overlapping p orbitals. Describe the difference.

Answer: Sigma bonds are formed from the overlap of atomic orbitals along a circular axis of symmetrical nature, i.e., head-on overlap. All single bonds are sigma bonds. Pi bonds are formed from the overlap of atomic orbitals along a non-symmetrical (parallel) axis, i.e., side-to-side overlap. Double and triple bonds contain both sigma and pi bonds.

Why is the C-H bond in ethene (H2C=CH2) shorter and stronger than the C-H bond in ethane(CH3CH3)?

Answer: The length and strength of a C-H bond depends on the hybridization of the carbon atom. The more s character in the hybrid orbital used by carbon to form the bond, the shorter and stronger the bond. This is because an s orbital is closer to the nucleus than is a p. Ethene uses carbon sp2 hybrid orbitals (1/3 s character) to make its carbon-hydrogen bonds while ethane uses carbon sp3 (1/4 s character).

32) The N-H single bond in methyl amine (CH3NH2) is a __________ bond formed by the overlap of a__________ orbital on N and a __________ on H. A) σ; sp2; s B) σ ; sp3 ; s C) π ; sp3 ; s D) π ; sp2 ; p E) π ; p ; p

B

35) Among the hydrogen halides, the strongest bond is found in __________ and the longest bond is found in __________. A) HF, HF B) HF, HI C) HI, HF D) HI, HI E) HCl, HBr

B

6.) Which of the following statements correctly describes the third electron shell that surrounds the nucleus of an atom? A) The third shell contains only s and p atomic orbitals. B) The maximum number of electrons that can occupy the third shell is 18. C) The total number of atomic orbitals present in the third shell is 16. D) The third shell can contain f orbitals. E) All third shell elements must have d electrons.

B

flip for question Answer: D

39) What is the CNN bond angle in the compound shown below? A) ~60° B) ~90° C) ~110° D) ~120° E) ~180°

Ar, K+, Cl- are isoelectronic elements (elements with the same number of electrons). What orbital does the last electron occupy?

3p orbital

flip for question Answer: B

50) The formal charge on nitrogen in the compound below is __________. A) +2 B) +1 C) 0 D) -1 E) -2

flip for question answer: E

53) What are the formal charges on nitrogen and the starred oxygen atom in the following molecule? A) N = -1, O = 0 B) N = +1, O = -1 C) N = +1, O = +1 D) N = -1, O = -1 E) N= +1, O = 0

flip for question Answer: CH3(CH2)3CH3

9) The Kekulé structure of pentane is shown below. Draw the condensed structural formula which corresponds to this Lewis structure. C5 H12- flip to see the picture

27) What is the predicted shape, bond angle, and hybridization for +CH3? A) trigonal planar, 120°, sp2 B) trigonal planar, 120°, sp3 C) trigonal planar, 109.5°, sp2 D) trigonal pyramidal, 120°, sp2 E) trigonal pyramidal, 109.5°, sp2

A

43) Which of the compounds below bond predominantly via ionic bonding? A) KCl B) CF4 C) NH3 D) both A and B E) both B and C

A

45) Which of the following contain(s) polar covalent bonds? A) NH3 B) Na2O C) H2 D) KF E) both A and C

A

56) Which of the following molecules has the smallest dipole moment? A) Br2 B) NH3 C) HCl D) HBr E) HI

A

Which of the following elements does this electronic configuration represent? 1s² 2s² 2p₅ a.) F b.) C c.) N d.) Al e.) O

A

Which of the following is an sp2 hybridized carbon? A) ⊕ CH3 B) · CH3 C) ⊖ :CH3 D) A and B E) A, B and C

A

Which of the following is the electronic configuration of the element Fe? A) 1s2 2s2 2p6 3s2 3p6 4s2 3d6 B) 1s2 2s2 2p6 3s2 3p8 3d6 C) 1s2 2s2 2p8 3s2 3p6 4s2 3d6 D) 1s2 2s2 2p6 3s2 3p6 4s2 4d6 E) 1s2 2s2 2p6 3s2 3p6 4s2 4p

A

The atomic number of boron is 5. The correct electron configuration of boron: A) 1s2 2s3 B) 1s2 2p3 C) 1s2 2s2 2p1 D) 2s2 2p3 E) 1s2 2s2 3s1

C

33) Triethylamine [(CH3CH2)3N] is a molecule in which the nitrogen atom is __________ hybridized and the CNC bond angle is __________. A) sp2, >109.5° B) sp2, <109.5° C) sp3, >109.5° D) sp3, <109.5° E) sp, 109.5°

D

38) The carbon-carbon double bond in ethene (H2C=CH2) is __________ and __________ than the carbon-carbon triple bond in ethyne(HC≡CH). A) stronger; shorter B) stronger; longer C) weaker; shorter D) weaker; longer E) stronger; more polar

D

42) The compound methylamine, CH3NH2, contains a C-N bond. In this bond, which of the following best describes the charge on the nitrogen atom? A) +1 B) slightly positive C) uncharged D) slightly negative E) -1

D

54) Which of the following molecules does not exhibit a net dipole moment of zero? A) CO2 B) CH4 C) CCl4 D) H2O E) SO3

D

flip for question answer: π

What kind of molecular orbital (σ, σ*, π, or π*) results when the two atomic orbitals shown below interact in the manner indicated?

flip for question answer: σ*

What kind of molecular orbital (σ, σ*, π, or π*) results when the two atomic orbitals shown below interact in the manner indicated?

flip for question Answer E

36) Which bond in the following molecule is the shortest? A) bond 1 B) bond 2 C) bond 3 D) bond 4 E) bond 5

flip for question Answer: B

37) Which of the following species have tetrahedral bond angles? A) A, D and E B) A, D, E and F C) A and E D) D only E) A, B and E

flip for question answer: σ

19) What kind of molecular orbital (σ, σ*, π, or π*) results when the two atomic orbitals shown below interact in the manner indicated?

flip for question answer: σ*

21) What kind of molecular orbital (σ, σ*, π, or π*) results when the two atomic orbitals shown below interact in the manner indicated?

flip for question answer: π*

22) What kind of molecular orbital (σ, σ*, π, or π*) results when the two atomic orbitals shown below interact in the manner indicated?

flip for question answer: E

25) Which carbon(s) in the following molecule is (are) sp hybridized? A) carbon 1 B) carbon 2 C) carbons 1, 3 D) carbons 4 E) carbon 4, 5

16) Consider the interaction of two hydrogen 1s atomic orbitals of the same phase. Which of the statements below is an incorrect description of this interaction? A) A sigma bonding molecular orbital is formed. B) The molecular orbital formed is lower in energy than a hydrogen 1s atomic orbital. C) The molecular orbital formed has a node between the atoms. D) The molecular orbital formed is cylindrically symmetric. E) A maximum of two electrons may occupy the molecular orbital formed.

C

30) Which of the following is closest to the C-O-C bond angle in CH3-O-CH3? A) 180° B) 120° C) 109.5° D) 90° E) 160°

C

44) What type of bonding is most important in CH3CH2CH2CH2CH2CH3? A) ionic B) hydrogen C) covalent D) polar

C

Choose the correct hybridization for the atom indicated in the molecule below. CH3CH2CH2CH3 ↑ A) sp B) sp2 C) sp3 D) none of the above

C

How many unpaired electrons are present in the isolated carbon atom (atomic number= 6)? a.) none b.) one c.) two d.) three e.) four

C

14) How many distinct and degenerate p orbitals exist in the second electron shell, where n = 2? A) 0 B) 1 C) 2 D) 3 E) 4

D

28) What orbitals overlap to create the H-C bond in CH3+? A) sp3-sp3 B) sp2-sp3 C) s-p D) s-sp2 E) s-sp3

D

29) The lone-pair electrons of the oxygen in H 2O occupy a __________ orbital. A) s B) p C) sp D) sp2 E) sp3

E

31) Each lone pair of electrons on the O atom in methanol (CH3OH) occupies a(n) __________ orbital A) s B) p C) sp D) sp2 E) sp3

E

34) The N-H bond in the ammonium ion, NH4+, is formed by the overlap of what two orbitals? A) sp3-sp3 B) sp3-sp2 C) sp2-sp2 D) sp2-s E) sp3-s

E

46) Which of the following covalent bonds has the largest dipole moment? A) C-C B) C-H C) C-O D) H-N E) H-F

E

What orbitals are used to form the covalent bonds in butane (CH3CH2CH2CH3)?

The carbon-carbon σ bonds are formed by the overlap of two carbon sp3 hybrid atomic orbitals. The carbon-hydrogen σ bonds are formed by the overlap of a carbon sp3 hybrid atomic orbital and a hydrogen s orbital

48) Covalent bonds may be polar or nonpolar. What property of the atoms forming a given bond determines this?

electronegativity

Atoms with the same number of protons but different numbers of neutrons are called________.

isotopes

49) Provide the mathematical equation for the dipole moment of a bond, and identify the variables.

μ = e × d, where μ is the bond dipole moment, e is the amount of charge which is separated, and d is the distance over which the charge is separated