A subject of the type 'the sentence to describe this situation...' is impossible in the English grammar. The theory behind such statement is very complex. It seems that the article from a grammar site could be useful.
The complement in an adjectival phrase of the type 'to describe this situation... " is quite possible.
That is why the first sentence is just ungrammatical, the second is grammatical.
It seems to be useful concerning the question, article.
'To my mind, it's better to start learning the language with a non-native speaker and then when the basic lever has been learnt, then it's necessary to continue studying with a native speaker in order to get better pronunciation and the speaking&listening skills'. (a quotation)
It is essential to add to the citation from this article that natives are prone to think in paragraphs and discourse of the mother-tongue and speak bearing such elements of speech in mind most of all unconsciously, but nonnatives are prone to think in sentences being made consciously in the moments of speaking by translating them from their mother-tongues. Usually the nonnatives are guided by the paragraphs and discourse made in their mother-tongues being kept unconsciously in their minds.
All this makes the difference. The natives do not need a detailed knowledge of the grammar of own language very often, not to say usually, in everyday life. But, it is not the case when we consider such discourses as engeneering and academic, for example. Written with respect to everyone concerned.