Part of speech identification

Hello, this is my first post here, I like to know these words
kilometer
centimeter

Are those words noun if they are standing alone ? if it's, what kind of noun it's, proper noun or abstract noun or etc ?

After that, I want to indentify the part of speech of the following sentence by using the stanford parser at http://nlp.stanford.edu:8080/parser/index.jsp
if you input,
convert kilometer to centimeter
it gives convert/VB kilometer/NN to/TO centimeter/VB

if you input,
convert 2 kilometers to centimeter
it gives convert/VB 2/CD kilometers/NNS to/TO centimeter/NN

You can refer to the tagset below, my question is, is the first input grammatically correct ? if it's correct the part of speech given by the program seems to be incorrect because
the centimeter should be noun instead of Verb, or am I wrong ? If you add the "2" as the second input the program gives the correct part of speech tagging,
is it because my first input grammar is incorrect ? Thank you.

Reference
1. CC Coordinating conjunction 25.TO to
2. CD Cardinal number 26.UH Interjection
3. DT Determiner 27.VB Verb, base form
4. EX Existential there 28.VBD Verb, past tense
5. FW Foreign word 29.VBG Verb, gerund/present participle
6. IN Preposition/subord. 30.VBN Verb, past participle
218z conjunction
7. JJ Adjective 31.VBP Verb, non-3rd ps. sing. present
8. JJR Adjective, comparative 32.VBZ Verb, 3rd ps. sing. present
9. JJS Adjective, superlative 33.WDT wh-determiner
10.LS List item marker 34.WP wh-pronoun
11.MD Modal 35.WP Possessive wh-pronoun
12.NN Noun, singular or mass 36.WRB wh-adverb
13.NNS Noun, plural 37. # Pound sign
14.NNP Proper noun, singular 38. $ Dollar sign
15.NNPS Proper noun, plural 39. . Sentence-final punctuation
16.PDT Predeterminer 40. , Comma
17.POS Possessive ending 41. : Colon, semi-colon
18.PRP Personal pronoun 42. ( Left bracket character
19.PP Possessive pronoun 43. ) Right bracket character
20.RB Adverb 44. " Straight double quote
21.RBR Adverb, comparative 45. ` Left open single quote
22.RBS Adverb, superlative 46. " Left open double quote
23.RP Particle 47. ' Right close single quote
24.SYM Symbol 48. " Right close double quote